Titanium composite material and titanium material for hot working

ABSTRACT

Provided is a titanium composite material  1  including: a first surface layer portion  2 ; an inner layer portion  4 ; and a second surface layer portion  3 ; wherein: the first surface layer portion  2  and the second surface layer portion  3  are composed of a titanium alloy; the inner layer portion  4  is composed of a commercially pure titanium including pores; a thickness of at least one of the first surface layer portion  2  and the second surface layer portion  3  is 2 μm or more, and a proportion of the thickness with respect to an overall thickness of the titanium composite material  1  is 40% or less; and a porosity in a cross section perpendicular to a sheet thickness direction is more than 0% and 30% or less.

TECHNICAL FIELD

The present invention relates to a titanium composite material and atitanium material for hot working.

BACKGROUND ART

A titanium material is excellent in properties such as corrosionresistance, oxidation resistance, fatigue resistance, hydrogenembrittlement resistance, and neutron blocking properties. Theseproperties can be attained by adding various alloying elements totitanium.

Because a titanium material is light weight and excellent in corrosionresistance, for example, a titanium material is utilized forseawater-cooled condensers at power generating plants, heat exchangersfor ocean water desalinization plants, reaction vessels of chemicalplants and also for coolers and the like.

Commercially pure titanium exhibits excellent corrosion resistanceparticularly in environments including nitrate or chromate or the like,and environments including seawater or chloride ions and the like.However, in environments including hydrochloric acid, sulfuric acid orthe like, a high corrosion resistance cannot be expected, and inenvironments including chlorine ions or the like, crevice corrosionsometimes occurs.

Therefore, various kinds of alloys, such as Ti-0.2Pd (ASTM Gr. 7, 11),are being developed in which trace amounts of platinum group elements(Ru, Rh, Pd, Os, Ir, Pt and the like) are added to titanium. Further,corrosion resistant titanium alloys that are inexpensive and excellentin corrosion resistance, such as Ti-0.5Ni-0.05Ru in which Ni and Ru aresubstituted for Pd, are also being developed.

A titanium material is excellent in specific strength and corrosionresistance, and hence utilization of titanium material in the field ofaircraft construction is progressing, and titanium material is alsobeing widely used for exhaust systems of automobiles and two-wheeledvehicles. In particular, from the viewpoint of reducing the weight ofvehicles, a commercially pure titanium material of JIS Class 2 is beingused instead of the conventional stainless steel material for vehicleproduction centering on two-wheeled vehicles. In addition, in recentyears, a heat-resistant titanium alloy having a higher heat resistanceis being used in place of commercially pure titanium material of JISClass 2. Furthermore, titanium material is also being used for mufflersin which a catalyst that is used at a high temperature is mounted forthe purpose of removing harmful components in exhaust gas.

The temperature of exhaust gas exceeds 700° C., and in some cases thetemperature temporarily reaches 800° C. Consequently, material to beused for an exhaust system is required to have strength, oxidationresistance and the like at a temperature of around 800° C., andfurthermore, importance is placed on the index of high-temperature heatresistance with respect to the creep rate at 600 to 700° C.

On the other hand, to improve the high temperature strength of suchheat-resistant titanium alloys, it is necessary to add elements thatimprove high temperature strength and oxidation resistance such as Al,Cu and Nb, and the cost of the heat-resistant titanium alloys is high incomparison to commercially pure titanium.

JP2001-234266A (Patent Document 1) discloses a titanium alloy that isexcellent in cold workability and high temperature strength, and thatcontains Al: 0.5 to 2.3% (in the present description, unless otherwisespecified, “%” with respect to chemical composition means “masspercent”).

JP2001-89821A (Patent Document 2) discloses a titanium alloy that isexcellent in oxidation resistance and corrosion resistance, and thatcontains Fe: more than 1% to 5% and O (oxygen): 0.05 to 0.75%, and alsocontains Si: 0.01·e^(0.5[Fe]) to 5·e^(−0.5[Fe]) ([Fe] represents content(mass %) in the alloy, and “e” represents base of natural logarithm).

JP2005-290548A (Patent Document 3) discloses a heat-resistant titaniumalloy plate that is excellent in cold workability and that contains Al:0.30 to 1.50% and Si: 0.10 to 1.0%, and a method for producing theheat-resistant titanium alloy plate.

JP2009-68026A (Patent Document 4) discloses a titanium alloy thatcontains Cu: 0.5 to 1.8%, Si: 0.1 to 0.6%, and O: 0.1% or less, and asnecessary contains Nb: 0.1 to 1.0%, with the balance being Ti andunavoidable impurities, and having a protective film coated on thesurface thereof.

In addition, JP2013-142183A (Patent Document 5) discloses a titaniumalloy that is excellent in high temperature strength at 700° C. and inoxidation resistance at 800° C. that contains Si: 0.1 to 0.6%, Fe: 0.04to 0.2% and O: 0.02 to 0.15% and in which the total content of Fe and Ois 0.1 to 0.3%, with the balance being Ti and unavoidable impurityelements.

A titanium cold-rolled sheet or plate (hereinafter referred to as“sheet”) product for industrial use (for example, a commercially puretitanium cold-rolled sheet product) is used, for example, by forming asheet product into a predetermined shape such as in the case of asheet-type heat exchanger or an FC separator, and the uses thereof areexpanding. Consequently, in addition to formability, thinning that isachieved by an improvement in fatigue strength, as well as a highadditional environment (under a high load) are also required fortitanium cold-rolled sheet products for industrial use.

On the other hand, similarly to other metallic materials, in the case ofpure titanium, there is a contrary relation between ductility, whichgoverns formability, and strength (fatigue strength).

JP2008-195994A (Patent Document 6) discloses a method that performssurface modification of a product made of titanium to improve fatiguestrength by performing a plasma nitriding process that performs plasmanitriding which takes a product made of any of pure titanium, an α-typetitanium alloy, a β-type titanium alloy and an α+β-type titanium alloyas a treatment object to form a hardened layer on the surface of thetreatment object, and then removes a compound layer that is present onthe surface of the hardened layer by performing a fine particlebombardment treatment in which the treatment object is subjected tobombardment with one or more kinds of fine particles after the plasmanitriding process.

JP2013-76110A (Patent Document 7) discloses a surface treatment methodfor treating a surface of a substrate consisting of a titanium alloy andtitanium, the method including a step A of subjecting the surface of asubstrate made of titanium alloy and titanium to a fine particle peeningprocess, a step B of performing a first heat treatment in a temperaturerange T1, a step C of performing a second heat treatment in atemperature range T2, and a step D of performing a third heat treatmentin a temperature range T3 which are performed in the order mentioned,which satisfies the relation T1>T2>T3, and in which T1 is made atemperature from 900 to 1000° C. That is, this surface treatment methodimproves fatigue strength by forming, in a region in the vicinity of thesurface of a titanium material, an amorphous layer, a fine grain layer(α phase; grain diameter: approximately 300 nm), a sub-micron grainlayer (α phase; grain diameter: approximately 500 nm), and a microngrain layer (β phase; grain diameter: approximately 3000 nm) in theorder from the surface side.

A commercially pure titanium contains the α phase of an hcp (hexagonalclose-packed) structure as a main constituent, and it is known that if alarge amount of hydrogen is absorbed in the α phase, hydrides will beformed and the commercially pure titanium will become brittle.Therefore, depending on the usage environment, in some cases accidentsoccur in which commercially pure titanium absorbs hydrogen and becomesbrittle and ruptures. In “CHITAN NO KAKOU GIJYUTSU” (Non-Patent Document1), for example, accidents caused by absorption of hydrogen at a planthandling a nonoxidizing acid or in a urea-ammonia environment and ahydrogen gas environment are reported. Therefore, a titanium alloyproduct that is excellent in hydrogen embrittlement resistance isproposed.

JP2013-163840A (Patent Document 8) discloses a titanium alloy thatexhibits large breaking elongation and that contains 50% or more byvolume of β phase and contains 500 to 6000 ppm of hydrogen, and anexample is described in which embrittlement does not occur even when alarge amount of hydrogen is contained.

A neutron shielding sheet that is capable of shielding from thermalneutrons is used at facilities that handle radioactive waste such asfacilities related to nuclear power generation. A neutron shieldingeffect is highest in boron 10 (¹⁰B) whose abundance is 19.9% in naturalB. Stainless steel or the like containing B is generally used asmaterial for a neutron shielding sheet.

JP58-6704B (Patent Document 9) discloses a neutron blocking materialthat contains 5% by mass or more of B, which is a cured compact formedby kneading and molding a borate aggregate containing crystal water suchas kurnakovite (2MgO.3B₂O₂.13H₂O), Meyerhof-ferrite (3CaO.3B₂O₂.7H₂O),or colemanite (2CaO.3B₂O₂.5H₂O), hemihydrate gypsum, and an inorganicadhesive agent such as a calcium aluminate-based cement with water.Patent Document 9 discloses, however, the neutron shielding materialincluding cement, there are problems in terms of corrosion resistance,producibility and also workability.

The use of a boron-containing titanium alloy that is superior incorrosion resistance to stainless steel as a neutron blocking materialis also being studied. For example, JP1-168833B (Patent Document 10)discloses the use of a heat-rolled plate made of a boron-containingtitanium alloy which contains 0.1 to 10% by mass of B with the balancebeing titanium and unavoidable impurities.

In addition, JP5-142392A (Patent Document 11) discloses a radiationshielding material in which a fluid of a boron-containing substance(NaB₄O₇, B₂O₃ or PbO, Fe₂O₃ or the like) and metallic oxides that aremixed therein are filled within a hollow metal casing and made into asolidified state. According to Patent Document 11, neutrons are blockedby mainly boron and hydrogen, and gamma rays are blocked by the casing,the metal and the like therein.

A titanium material is normally produced by the following method. First,using the Kroll process, titanium oxide as the raw material ischlorinated to form titanium tetrachloride, and thereafter is reducedusing magnesium or sodium to produce massive and sponge-like titaniummetal (titanium sponge. The titanium sponge is subjected topress-forming to form a consumable titanium electrode, and a titaniumingot is produced by vacuum arc melting that adopts the consumabletitanium electrode as an electrode. At such time, alloying elements areadded as required to produce a titanium alloy ingot. Thereafter, thetitanium alloy ingot is bloomed, forged and rolled to form a titaniumslab, and the titanium slab is further subjected to hot rolling,annealing, pickling, cold rolling, and a vacuum heat treatment toproduce a titanium sheet.

Further, as a method for producing a titanium sheet, a method is alsoknown in which a titanium ingot is subjected to blooming,hydrogenation-crushing, dehydrogenation, pulverization and classifyingto produce a titanium powder, and thereafter the titanium powder issubjected to powder rolling, sintering and cold rolling to produce atitanium sheet.

JP2011-42828A (Patent Document 12) discloses a method for producing atitanium sheet, in which a titanium powder is produced directly fromtitanium sponge and not a titanium ingot, and in order to produce atitanium sheet from the obtained titanium powder, a pre-sinteringcompact in which a viscous composition containing a titanium metalpowder, a binding agent, a plasticizer and a solvent is formed in asheet shape is sintered to produce a sintered sheet, the sintered sheetis consolidated to produce a sintered and consolidated sheet, and thesintered and consolidated sheet is then re-sintered, in which thebreaking elongation of the sintered sheet is 0.4% or more, the densityratio of the sintered sheet is 80% or more, and the density ratio of thesintered and consolidated sheet is 90% or more.

JP2014-19945A (Patent Document 13) discloses a method for producing atitanium alloy that is excellent in quality by a powder method, in whicha suitable amount of iron powder, chromium powder or copper powder isadded to a titanium alloy powder for which titanium alloy scrap or atitanium alloy ingot is adopted as a raw material to thereby form acomposite powder, the composite powder is extruded from a carbon steelcapsule, and the capsule is melted and removed from the surface of anobtained round bar, and thereafter a solution treatment or a solutiontreatment and aging treatment are performed.

JP2001-131609A (Patent Document 14) discloses a method for producing atitanium compact, in which a copper capsule is packed with a titaniumsponge powder and thereafter subjected to a hot extrusion process at anextrusion ratio of 1.5 or more and an extrusion temperature of 700° C.or less and formed, an outer circumference process is performed toremove copper from the outside, and thereby obtain a titanium compact inwhich 20% or more of the total length of the grain boundary of thecompact is in contact with a metal.

When subjecting hot rolling material to hot rolling, in a case where thehot rolling material is a so-called “difficult-to-process material”which lacks ductility and has a high hot deformation resistance valueduring hot processing, such as pure titanium or a titanium alloy, apack-rolling method is known as a technique for rolling such materialsinto a sheet. The pack-rolling method is a method in which a corematerial such as a titanium alloy that has poor workability is coveredwith a cover material such as carbon steel that has good workability andis inexpensive, and hot rolling is then performed.

Specifically, for example, a release agent is coated on the surface ofthe core material, and at least the upper and lower two faces thereofare covered with a cover material, or in addition to the upper and lowerfaces, the four peripheral faces are covered by a spacer material, andthe circumference is welded and assembled and hot rolling is performed.In pack rolling, the core material that is the material to be rolled iscovered with a cover material and subjected to hot rolling. Therefore,because the core material surface is not directly touched by a coldmedium (atmospheric air or a roll) and therefore a decrease in thetemperature of the core material can be suppressed, production of asheet is possible even from a core material that has poor workability.

JP63-207401A (Patent Document 15) discloses a method for assembling asealed covered pack, JP09-136102A (Patent Document 16) discloses amethod for producing a sealed covered pack which is sealed with a covermaterial at a degree of vacuum of the order of 10⁻³ torr or more, andJP11-057810A (Patent Document 17) discloses a method for producing asealed covered pack which is covered with a carbon steel (covermaterial) and sealed by high-energy density welding under a vacuum ofthe order of 10⁻² torr or less.

On the other hand, as a method for inexpensively producing materialhaving high corrosion resistance, a method is known for joining atitanium material to the surface of material that serves as a basemetal.

JP08-141754A (Patent Document 18) discloses a method for producing atitanium clad steel plate, in which a steel material is used as a basemetal and titanium or a titanium alloy is used as a cladding material,and in which assembled slabs for rolling that were assembled by weldingthe joining surfaces of the base metal and cladding material after beingevacuated of air, are joined by hot rolling.

JP11-170076A (Patent Document 19) discloses a method for producing atitanium covered steel material by laminating and disposing a titaniumfoil material on the surface of a steel material as a base metal thatcontains 0.03% by mass or more of carbon with, interposed therebetween,an insert material having a thickness of 20 μm or more that consists ofany one of low-carbon steels in which the content of pure nickel, pureiron and carbon is 0.01% by mass or less, and thereafter irradiating alaser beam from any one side in the lamination direction to melt andjoin at least the vicinity of the edges of the titanium foil materialand the steel material as the base metal over the entire circumference.

In addition, JP2015-045040A (Patent Document 20) exemplifies a methodfor producing, using very little energy, dense titanium material (atitanium ingot) including a porous portion formed by forming a poroustitanium raw material (titanium sponge) into an ingot shape, and a densecoating portion that is constituted by dense titanium and that coversthe entire surface of the porous portion, by producing a titanium ingotby melting the surface of the porous titanium raw material formed in aningot shape using an electron beam under vacuum to turn a surface layerportion into dense titanium, and subjecting the titanium ingot to hotrolling and cold rolling.

LIST OF PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP2001-234266A-   Patent Document 2: JP2001-89821A-   Patent Document 3: JP2005-290548A-   Patent Document 4: JP2009-68026A-   Patent Document 5: JP2013-142183A-   Patent Document 6: JP2008-195994A-   Patent Document 7: JP2013-76110A-   Patent Document 8: JP2013-163840A-   Patent Document 9: JP58-6704B-   Patent Document 10: JP1-168833B-   Patent Document 11: JP5-142392A-   Patent Document 12: JP2011-42828A-   Patent Document 13: JP2014-19945A-   Patent Document 14: JP2001-131609A-   Patent Document 15: JP63-207401A-   Patent Document 16: JP09-136102A-   Patent Document 17: JP11-057810A-   Patent Document 18: JP08-141754A-   Patent Document 19: JP11-170076A-   Patent Document 20: JP2015-045040A

Non Patent Document

-   Non-Patent Document 1: CHITAN NO KAKOU GIJYUTSU, (SHA) NIHON CHITAN    KYOUKAI HEN, NIKKAN KOUGYOU SHINBUNSHA, p. 214-230, published    November 1992

SUMMARY OF INVENTION Technical Problem

As described in the foregoing, because titanium alloys in whichcorrosion resistance is improved contain platinum group elements whichare scarce and expensive, the production cost of the titanium alloysincreases significantly.

Patent Document 1 discloses the titanium alloy to which Al is added,there is an adverse effect on forming workability, particularly onbulging formability when the working occurs in a direction in which thewall thickness decreases.

Patent Document 2 discloses the titanium alloy the total content of Feand O of which is large, the strength at room temperature is more than800 N/mm² which is a value that is too strong, and consequently theformability is poor, with elongation being not more than 20%.

Patent Document 3 discloses the titanium alloy to which Al is added,similarly to the titanium alloy described above, there is a risk ofadversely affecting cold workability, particularly on bulgingformability when the working occurs in a direction in which the wallthickness decreases.

Patent Document 4 discloses the titanium alloy having sufficientworkability and oxidation resistance properties, because the titaniumalloy contains a large amount of Nb which is expensive, the alloy costincreases.

In addition, Patent Document 5 discloses the titanium alloy havingsufficient high-temperature oxidation properties, the alloy costincreases because the entire plate surface is alloyed.

Patent Document 6 discloses the method, in which although C and N whichhave a high solid-solution strengthening ability are used for formationof a hardened layer and consequently the titanium hardens and thefatigue strength can be improved when the C and N are dissolved, thisresults in a rapid decrease in ductility, and hence the formability ispoor.

Further, according to the results of studies conducted by the presentinventors, Patent Document 7 discloses the surface treatment method, bymeans of which is not easy to improve formability.

In addition, Patent Documents 6 and 7 disclose the inventions, in whichit is necessary to perform a special surface treatment on a titaniummaterial, and an increase in the production cost is unavoidable.

As a measure to counter embrittlement caused by hydrogen, generally asurface treatment that provides hydrogen absorption resistance isperformed after working into a finished product, or electrolyticprotection is carried out with respect to the finished product. However,both of these cases involve an increase in product working or in theman-hours for working and the like, and consequently an increase in costis unavoidable, and a titanium material that is excellent in hydrogenembrittlement resistance cannot be provided at a low cost.

Further, Patent Document 8 discloses the method in which, in order tomake 50% or more by volume of the entire material β phase, it isnecessary for a large amount of expensive additional elements to becontained, and hence the cost increases.

Patent Document 10 discloses the heat-rolled plate the B content inwhich is high, it cannot be denied that the cost increases, and theworkability is also not favorable, and the use thereof as a neutronshielding plate is difficult in practice.

In addition, Patent Document 12 discloses the radiation shieldingmaterial in which a casing material made of metal is packed with aboron-containing substance, and working thereof is difficult after theboron-containing substance has been supplied.

Conventionally, when producing a titanium material by way of hotworking, titanium sponge is press-formed to form a consumable titaniumelectrode, a titanium ingot is produced by performing vacuum are meltingthat adopts the consumable titanium electrode as an electrode, thetitanium ingot is then subjected to blooming, forging and rolling toform a titanium slab, and the titanium slab is subjected to hot rolling,annealing, pickling and cold rolling to produce the titanium material.

In this case, a process of melting titanium to produce a titanium ingothas been invariably added. Although a method for producing a titaniummaterial by subjecting titanium powder to powder rolling, sintering, andcold rolling is also known, a method for producing titanium powder froma titanium ingot has also included a process of melting titanium.

In a method for producing a titanium material from titanium powder, evenif a melting process is not undergone, the obtained titanium material isextremely expensive because expensive titanium powder is used as rawmaterial. Patent Documents 15 and 16 disclose the methods with respectto which the situation similarly applies.

In pack rolling, a core material to be covered by a cover material ismerely a slab or an ingot, and undergoes a melting process or adoptsexpensive titanium powder as a raw material, and hence the productioncost cannot be reduced.

According to Patent Document 20, although a dense titanium material canbe produced using an extremely small amount of energy, according to thismethod the surface of titanium sponge formed in an ingot shape is meltedand the surface layer portion and internal components of the densetitanium are specified as pure titanium or a titanium alloy of the samegrade, and for example it is not possible to reduce the production costby forming a titanium alloy layer uniformly over a wide range on onlythe surface layer portion.

On the other hand, with respect to a material obtained by joiningtitanium or a titanium alloy to the surface of a base metal as a methodthat can produce an inexpensive corrosion-resistant material, in manycases steel is selected as the base metal. Therefore, if the titaniumlayer on the surface is lost, the corrosion resistance will also belost. Even if a titanium material is adopted as the base metal, as longas a titanium material is used that is produced by undergoing a normalproduction process, a dramatic improvement in cost cannot be expected.

An objective of the present invention is to inexpensively obtain atitanium material having desired characteristics, by reducing thecontent of alloying elements (usage amount of specific alloying elementsthat exhibit target characteristics) added to improve variouscharacteristics required of a titanium material such as corrosionresistance, oxidation resistance, fatigue resistance, hydrogenembrittlement resistance, and neutron blocking properties, and to reducethe production cost of the titanium material.

Solution to Problem

The present invention was made to solve the problems described above,and the gist of the present invention is a titanium composite materialand a titanium material for hot working which are described hereunder.

(1) A titanium composite material comprising:

a first surface layer portion;

an inner layer portion; and

a second surface layer portion;

wherein:

the first surface layer portion and the second surface layer portionconsist of a titanium alloy;

the inner layer portion consists of a commercially pure titaniumincluding pores;

a thickness of at least one of the first surface layer portion and thesecond surface layer portion is 2 μm or more, and a proportion of thethickness with respect to an overall thickness of the titanium compositematerial is 40% or less; and

a porosity in a cross section perpendicular to a sheet thicknessdirection is more than 0% and 30% or less.

(2) The titanium composite material according to (1) above, wherein

at least one of the first surface layer portion and the second surfacelayer portion has a chemical composition comprising, by mass %:

platinum group elements: 0.01 to 0.25%,

rare earth elements: 0 to 0.2%,

Co: 0 to 0.8%,

Ni: 0 to 0.6%, and

a balance: Ti and impurities.

(3) The titanium composite material according to (2) above, wherein:

the platinum group elements are Pd and/or Ru.

(4) The titanium composite material according to (2) or (3) above,wherein

the chemical composition contains, by mass %:

rare earth elements: 0.001 to 0.2%.

(5) The titanium composite material according to any one of (2) to (4)above, wherein

the chemical composition contains, by mass % one or more elementsselected from:

Co: 0.05 to 0.8%, and

Ni: 0.05 to 0.6%.

(6) The titanium composite material according to any one of (1) to (5)above, wherein

the commercially pure titanium has a chemical composition comprising, bymass %,

C: 0.1% or less,

H: 0.015% or less,

O: 0.4% or less,

N: 0.07% or less,

Fe: 0.5% or less, and

a balance: Ti and impurities.

(7) A titanium material for hot working, comprising:

a package; and

one or more types selected from a titanium sponge, a briquette obtainedby compressing a titanium sponge, and a commercially pure titaniumscrap, with which the package is packed,

wherein

a portion of the package consists of a titanium alloy, the portionconstituting an outer layer after hot working.

(8) The titanium material for hot working according to (7) above,wherein

the titanium alloy has a chemical composition comprising, by mass %,

platinum group elements: 0.01 to 0.25%,

rare earth elements: 0 to 0.2%,

Co: 0 to 0.8%,

Ni: 0 to 0.6%, and

a balance: Ti and impurities.

Advantageous Effects of Invention

A titanium composite material according to the present inventionincludes a surface layer portion consisting of a titanium alloy, and aninner layer portion consisting of a commercially pure titanium, andtherefore, although having equivalent characteristics to a titaniummaterial that consists entirely of the same titanium alloy, the titaniumcomposite material according to the present invention can beinexpensively produced in comparison to the titanium material thatconsists entirely of the same titanium alloy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory drawing illustrating one example of thestructure of a titanium composite material according to the presentinvention.

FIG. 2 is an explanatory drawing illustrating the structure of atitanium material as a material for hot working for the titaniumcomposite material according to the present invention.

FIG. 3 is an explanatory drawing illustrating a plane bending fatiguetest material.

FIG. 4 illustrates an example of microstructure photographs in the caseof manufacturing by a method described in the present specification.

FIG. 5 is a schematic diagram of a titanium material including atitanium sponge and scraps packing within a package that is madeslab-like by assembling Ti—B alloy sheets.

DESCRIPTION OF EMBODIMENTS

To solve the problems described above, the present inventor conductedintensive studies with respect to decreasing the usage amount ofspecific alloying elements that exhibit target characteristics byalloying only a surface layer portion of a titanium sheet of an endproduct and reducing the cost of producing the titanium material. As aresult, the present inventors discovered a method for producing atitanium composite material by packing and enclosing a relativelyinexpensive material such as titanium sponge in a package made oftitanium alloy products under a reduced pressure, and subjecting thetitanium materials to hot working.

The present invention was made based on the above findings. Hereunder,the titanium composite material and a titanium material for hot rollingthereof according to the present invention are described while referringto the accompanying drawings. Note that, in the following description,unless otherwise specified, “%” relating to the content of each elementmeans “mass percent”.

1. Titanium Composite Material

1-1. Overall Structure

As illustrated in FIG. 1, a titanium composite material 1 according tothe present invention includes a first surface layer portion 2, an innerlayer portion 4, and a second surface layer portion 3, the first surfacelayer portion 2 and the second surface layer portion 3 consist of atitanium alloy, and the inner layer portion 4 consists of a commerciallypure titanium in which pores are present. Corrosion resistance and othercharacteristics of the titanium composite material are ensured in thisway by surface layer portions (the first surface layer portion 2 and thesecond surface layer portion 3) that contact the external environment.Further, the first surface layer portion 2 and the second surface layerportion 3 are constituted by the titanium alloy of which variousperformances are superior to those of a commercially pure titanium.

Although having equivalent characteristics to a titanium material thatconsists entirely of the same titanium alloy, the titanium compositematerial 1 can be inexpensively produced in comparison to the titaniummaterial that consists entirely of the same titanium alloy.

1-2. First Surface Layer Portion and Second Surface Layer Portion

As described above, the first surface layer portion 2 and the secondsurface layer portion 3 consist of a titanium alloy. A particular limitis not set with respect to the chemical composition of the titaniumalloy. It is known that titanium alloys are generally classified into αtype, α+β type and β type. Further, it is known that Al, O, N and thelike are available as α stabilizing elements, V, Mo, Cr, Fe, Nb, Ta andthe like are available as β stabilizing elements, and Zr, Sn, Hf and thelike are available as neutral elements that do not belong to either theα stabilizing elements or β stabilizing elements.

Table 1 shows elements which, when contained in a titanium alloy, areknown to contribute to improving the characteristics of the titaniumalloy. A titanium alloy according to the present invention can impart atarget function to the surface of a titanium material by containing, forexample, by mass %, more than 0% of one or more types of elementselected from: O: 0 to 0.5%, N: 0 to 0.2%, C: 0 to 2.0%, Al: 0 to 8.0%,Sn: 0 to 10.0%, Zr: 0 to 20.0%, Mo: 0 to 25.0%, Ta: 0 to 5.0%, V: 0 to30.0%, Nb: 0 to 40.0%, Si: 0 to 2.0%, Fe: 0 to 5.0%, Cr: 0 to 10.0%, Cu:0 to 3.0%, Co: 0 to 3.0%, Ni: 0 to 2.0%, platinum group elements: 0 to0.5%, rare earth elements: 0 to 0.5%, B: 0 to 5.0%, and Mn: 0 to 10.0%.

Elements which can be contained in titanium which are other than theabove elements are elements that can improve strength by solid-solutionstrengthening or precipitation strengthening (there are cases whereelements do not dissolve and cases where elements cause a precipitate toform), or depending on the element that is contained, can improve creepcharacteristics, which are known as common knowledge pertaining to metalmaterials. Elements from, in terms of atomic number, hydrogen (1) toastatine (85) (however, excluding the noble gas elements that are Group18 elements) are exemplified as these elements, and up to approximately5% in total of these elements is allowed.

The balance other than the above elements is Ti and impurities. Theimpurities can be contained in a range that does not inhibit the targetcharacteristics, and other impurities are impurity elements that mainlyget mixed in from the raw material or scrap and elements that get mixedin during production, with C, N, O, Fe, H, and the like being elementsthat are representative examples thereof, and in addition there areelements such as Mg and Cl that get mixed in from raw material, andelements such as Si, Al and S that get mixed in during production. It isconsidered that a range in which these elements do not inhibit thetarget characteristics of the present application is not more thanapproximately 2%.

Further, as shown in Table 1, the titanium alloy according to thepresent invention preferably contains, by mass %, one or more types ofelement selected from: O: 0.01 to 0.5%, N: 0.01 to 0.2%, C: 0.01 to2.0%, Al: 0.1 to 8.0%, Sn: 0.1 to 10.0%, Zr: 0.5 to 20.0%, Mo: 0.1 to25.0%, Ta: 0.1 to 5.0%, V: 1.0 to 30.0%, Nb: 0.1 to 40.0%, Si: 0.1 to2.0%, Fe: 0.01 to 5.0%, Cr: 0.1 to 10.0%, Cu: 0.3 to 3.0%, Co: 0.05 to3.0%, Ni: 0.05 to 2.0%, platinum group elements: 0.01 to 0.5%, rareearth elements: 0.001 to 0.5%, B: 0.01 to 5.0%, and Mn: 0.1 to 10.0%.

More preferably, the titanium alloy according to the present inventioncontains one or more types of element selected from: O: 0.02 to 0.4%, N:0.01 to 0.15%, C: 0.01 to 1.0%, Al: 0.2 to 6.0%, Sn: 0.15 to 5.0%, Zr:0.5 to 10.0%, Mo: 0.2 to 20.0%, Ta: 0.1 to 3.0%, V: 2.0 to 25.0%, Nb:0.15 to 5.0%, Si: 0.1 to 1.0%, Fe: 0.05 to 2.0%, Cr: 0.2 to 5.0%, Cu:0.3 to 2.0%, Co: 0.05 to 2.0%, Ni: 0.1 to 1.0%, platinum group elements:0.02 to 0.4%, rare earth elements: 0.001 to 0.3%, B: 0.1 to 5.0%, andMn: 0.2 to 8.0%, and further preferably contains one or more types ofelement selected from: O: 0.03 to 0.3%, N: 0.01 to 0.1%, C: 0.01 to0.5%, Al: 0.4 to 5.0%, Sn: 0.2 to 3.0%, Zr: 0.5 to 5.0%, Mo: 0.5 to15.0%, Ta: 0.2 to 2.0%, V: 5.0 to 20.0%, Nb: 0.2 to 2.0%, Si: 0.15 to0.8%, Fe: 0.1 to 1.0%, Cr: 0.2 to 3.0%, Cu: 0.3 to 1.5%, Co: 0.1 to1.0%, Ni: 0.1 to 0.8%, platinum group elements: 0.03 to 0.2%, rare earthelements: 0.001 to 0.1%, B: 0.2 to 3.0%, and Mn: 0.2 to 5.0%.

TABLE 1 (mass %) More Further Preferable preferable preferable Elementrange range range Main role Purpose O 0.01~0.5 0.02~0.4  0.03~0.3 Strength improvement N 0.01~0.2 0.01~0.15 0.01~0.1  Strength improvementC 0.01~2.0 0.01~1.0  0.01~0.5  Strength improvement Al  0.1~8.0 0.2~6.00.4~5.0 Strength improvement Sn  0.1~10.0 0.15~5.0  0.2~3.0 Strengthimprovement Zr  0.5~20.0  0.5~10.0 0.5~5.0 Strength and workabilityimprovement Mo  0.1~25.0  0.2~20.0  0.5~15.0 High-temperature strengthand corrosion resistance improvement Ta  0.1~5.0 0.1~3.0 0.2~2.0 Heatresistance, corrosion resistance improvement V  1.0~30.0  2.0~25.0 5.0~20.0 Strength improvement, micro- structure control Nb  0.1~40.00.15~5.0  0.2~2.0 Heat resistance, strength improvement Si  0.1~2.00.1~1.0 0.15~0.8  Heat resistance improvement Fe 0.01~5.0 0.05~2.0 0.1~1.0 Strength improvement, micro- structure control Cr  0.1~10.00.2~5.0 0.2~3.0 Strength improvement Cu  0.3~3.0 0.3~2.0 0.3~1.5Strength and workability improvement Co 0.05~3.0 0.05~2.0  0.1~1.0Corrosion resistance improvement, strength improvement Ni 0.05~2.00.1~1.0 0.1~0.8 Corrosion resistance improvement, strength Platinumgroup elements 0.01~0.5 0.02~0.4  0.03~0.2  Corrosion resistance such asPt and Pd improvement Rare earth elements such 0.001~0.5  0.001~0.3 0.001~0.1  Corrosion resistance as Sc and Y, mixed rare improvementearth elements (misch metal) B 0.01~5.0 0.1~5.0 0.2~3.0 Neutronshielding performance improvement Mn  0.1~10.0 0.2~8.0 0.2~5.0 Strengthimprovement

Further, for example, titanium alloys specified in JIS Standards thatare described hereunder can also be used.

JIS Class 11 to JIS Class 23 (JIS 4600 (2012) Titanium and titaniumalloys—Sheets, plates and strips): include Pd, Ru, Ni, Co or the like,and are excellent in corrosion resistance and crevice corrosionresistance.

JIS Class 50 (JIS 4600 (2012) Titanium and titanium alloys—Sheets,plates and strips): is Ti-1.5Al, and is excellent in corrosionresistance, hydrogen absorption resistance and heat resistance.

JIS Class 60 (JIS 4600 (2012) Titanium and titanium alloys—Sheets,plates and strips): is Ti-6Al-4V, and is a high strength titanium alloywith a high degree of versatility.

JIS Class 61 (JIS 4600 (2012) Titanium and titanium alloys—Sheets,plates and strips): is Ti-3Al-2.5V, and provides favorable weldabilityand formability and favorable machinability.

JIS Class 80 (JIS 4600 (2012) Titanium and titanium alloys—Sheets,plates and strips): is Ti-4Al-22V, and is a high strength titanium alloythat is excellent in cold workability.

Furthermore, apart from the above described titanium alloys, a titaniumalloy having a chemical composition that is not specified in JISStandards can also be used. Examples of such titanium alloys are listedbelow.

Titanium alloys having heat resistance: Ti-6Al-2Sn-4Zr-2Mo-0.08Si,Ti-6Al-5Zr-0.5Mo-0.2Si, Ti-8Al-1Mo-1V, and the like.

Low-alloy, high-strength titanium alloys: Ti-1 to 1.5Fe-0.3 to 0.5O-0.01to 0.04N and the like.

Low-alloy titanium alloys having heat resistance: Ti-1Cu, Ti-1Cu-0.5Nb,Ti-1Cu-1Sn-0.35Si-0.5Nb, and the like.

Titanium alloys excellent in creep resistance: Ti-6Al-2Sn-4Zr-6Mo andthe like.

Titanium alloys having high strength and good cold workability:Ti-15V-3Cr-3Sn-3Al, Ti-20V-4Al-1Sn, and the like.

Titanium alloys having high strength and high toughness: Ti-10V-2Fe-3Aand the like.

Titanium alloys excellent in wear resistance: Ti-6Al-4V-10Cr-3C and thelike.

Preferably, at least one of the first surface layer portion 2 and thesecond surface layer portion 3 (at least a surface layer portion thatcontacts the external environment) contains alloying elements thatexpress a target characteristic, with the balance being Ti andimpurities. The following elements are exemplified as alloying elementsthat express a target characteristic, although the present invention isnot limited to these elements.

(a) Alloying elements exhibiting corrosion resistance: by mass %, 0.01to 0.25% of platinum group elements (Pd and/or Ru), and as required,0.2% or less of rare earth elements, and furthermore, one or more typesof element selected from Co: 0.8% or less and Ni: 0.6% or less, and thelike.

(b) Alloying elements exhibiting oxidation resistance: one or more typesof element selected from 0.10 to 0.60% of Si, 0.1 to 2.0% of Nb, 0.3 to1.0% of Ta, and 0.3 to 1.5% of Al, and as required, one or more types ofelement selected from 1.5% or less of Sn, 1.5% or less of Cu, and 0.5%or less of Fe (however, in an amount of 2.5% or less in total).

(c) Alloying elements exhibiting fatigue resistance: one or more typesof element selected from Fe, Cr, Ni, Al and Zr in a total amount of 0.08to 1.0%.

(d) Alloying elements exhibiting hydrogen embrittlement resistance: oneor more types of element selected from Mo, V and Nb in a range of 8.0<Moequivalent<20.0 (where, Mo equivalent=Mo content (mass %)+V content(mass %)/1.5+Nb content (mass %)/3.6).

(e) Alloying element exhibiting neutron blocking properties: 0.1 to 3.0%of B.

The respective cases described in the foregoing (a) to (e) will now beindividually described.

(a) Case of Containing Alloying Elements Exhibiting Corrosion Resistance(Thickness)

If the thickness of surface layer portion contacting the externalenvironment among the first surface layer portion 2 and the secondsurface layer portion 3 is too thin, corrosion resistance will not beadequately obtained. Although the thickness of the first surface layerportion 2 and the second surface layer portion 3 changes depending onthe thickness of the material that is used for production and also on aworking ratio thereafter, a sufficient effect is exerted if thethickness is 2 μm or more. Therefore, a thickness of at least one of thefirst surface layer portion 2 and the second surface layer portion 3 (atleast a surface layer portion that contacts the external environment) ispreferably 2 μm or more, and more preferably 5 μm or more.

On the other hand, although there is not a problem with respect tocorrosion resistance if the first surface layer portion 2 and the secondsurface layer portion 3 are thick, the cost benefit will decrease sincethe proportion that the titanium alloy occupies with respect to theentire titanium composite material will increase. Therefore, thethickness of the first surface layer portion 2 and the second surfacelayer portion 3 with respect to the overall thickness of the titaniumcomposite material 1 is preferably 40% or less, respectively, and morepreferably is 30% or less.

The thickness of the first surface layer portion 2 and the secondsurface layer portion 3 of the titanium composite material 1 depend onthe thickness of a titanium alloy product constituting a package 6described later and on a working ratio in hot working performedthereafter. For example, when a titanium composite material 1 having athickness of 5 mm is produced by hot working a titanium material 5 forhot working having a thickness of 75 mm (simply referred to as a“titanium material 5” in the following description) including thepackage 6 constituted by titanium materials having a thickness of 10 mm,the thickness of each of the first surface layer portion 2 and thesecond surface layer portion 3 in the titanium composite material 1 isabout 667 μm, accounting for about 13% of the overall thickness of thetitanium composite material 1.

(Chemical Composition)

The titanium composite material 1 according to the present invention maycontain various alloying elements described hereunder to increase thecorrosion resistance of at least one of the first surface layer portion2 and the second surface layer portion 3 (at least a surface layerportion that contacts the external environment).

Platinum Group Elements: 0.01 to 0.25%

A platinum group element has an effect that lowers the hydrogenationvoltage of a titanium alloy and maintains the spontaneous potential inan immobile zone, and can be contained as an alloying element thatexhibits corrosion resistance. The corrosion resistance will beinsufficient if the content of the platinum group element (total contentin a case where a plurality of platinum group elements is contained) isless than 0.01%. Even if the content is more than 0.25%, a significantimprovement in corrosion resistance cannot be expected, and a content ofmore than 0.25% leads to a steep rise in the raw material cost. In thecase of containing platinum group elements, the content thereof is made0.01 to 0.25%. Preferably the content of platinum group elements is0.03% or more, more preferably is 0.05% or more, and a content of 0.20%or less is preferable, and more preferably is 0.15% or less.

Although the platinum group elements that may be used in the presentinvention are all useful elements that have an effect that increasescorrosion resistance of the titanium alloy, in particular it ispreferable to contain Pd for which the advantageous effect of improvingcorrosion resistance is high per percentage content. Further, Ru whichis relatively inexpensive can be used as a substitute for Pd.

If a rare earth elements are added to a titanium alloy containing aplatinum group element, the Ti and platinum group element will berapidly eluted when exposed to a corrosive environment, and theconcentration of the platinum group element in a solution in thevicinity of the titanium alloy will increase. As a result, precipitationof the platinum group element in the titanium alloy will be promoted,and the platinum group element can be efficiently precipitated even ifthe dissolved amount of titanium alloy is small, and this leads to animprovement in corrosion resistance.

Rare Earth Elements: 0 to 0.2%

Rare earth elements include Sc, Y, light rare earth elements (La to Eu),and heavy rare earth elements (Gd to Lu), and the above effect can beexpected when any of the rare earth elements are added. The same effectcan also be expected in a case where a mixture or compound of rare earthelements are used, such as mixed rare earth elements before separationand refining (misch metal, hereinafter simply referred to as “Mm”) or adidymium alloy (Nd—Pr alloy).

Taking into account the circumstances described above, it is notnecessary for the rare earth element that is added to be of only onekind, and it is considered that corrosion resistance will be improved bythe above effect even if a plurality of elements are contained at thesame time. In such a case, the total content of rare earth elementsmeans the total content of the aforementioned elements.

If the content of rare earth elements is excessive, the above effect issaturated, and hence not only will a further advantageous effect ofimproving corrosion resistance not be obtained, but the economicefficiency will also decrease. Therefore, in the case of containing rareearth elements, the content thereof is preferably 0.2% or less and morepreferably is 0.02% or less. On the other hand, in order to adequatelyobtain an advantageous effect of eluting Ti and platinum group elementsin an active state area of the titanium alloy and to promoteprecipitation of the platinum group elements onto the alloy surface, itis preferable to contain 0.001% or more of rare earth elements.

Co: 0 to 0.8%

Ni: 0 to 0.6%

Co and Ni are elements that improve the corrosion resistance of thetitanium alloy by changing a hydrogenation voltage, and extremely highcorrosion resistance is obtained by adding Co and Ni in combination witha platinum group element and/or a rare earth elements. However, even ifthe Co content is more than 0.8% or the Ni content is more than 0.6%,the effect is saturated, and this is not preferable from a viewpoint ofeconomic efficiency also. Therefore, when these elements are contained,the Co content is made 0.8% or less and the Ni content is made 0.6% orless. The Co content is preferably 0.7% or less, and the Ni content ispreferably 0.5% or less. To reliably obtain the above effect, it ispreferable to contain 0.05% or more of each of Co and Ni, and containing0.2% or more of each of Co and Ni is more preferable.

The balance other than the above elements is Ti and impurities. Theimpurities can be contained in a range that does not inhibit the targetcharacteristics, and other impurities include Cr, Ta, Al, V, Cr, Nb, Si,Sn, Mn, Mo, Cu, and the like as impurity elements that get mixed inmainly from scrap, and impurities are allowed as long as the amountthereof together with C, N, Fe, O and H that are the common impurityelements is 0.5% or less.

(b) Case of Containing Alloying Elements Exhibiting Oxidation Resistance(Thickness)

If the thickness of a surface layer portion contacting the externalenvironment among the first surface layer portion 2 and the secondsurface layer portion 3 is too thin, oxidation resistance will not beadequately obtained. Although the thickness of the first surface layerportion 2 and the second surface layer portion 3 changes depending onthe thickness of the material that is used for production and also on aworking ratio thereafter, a sufficient effect is exerted if thethickness is 5 μm or more. Therefore, a thickness of at least one of thefirst surface layer portion 2 and the second surface layer portion 3 (atleast a surface layer portion that contacts the external environment) ispreferably 5 μm or more, and more preferably 10 μm or more.

On the other hand, although there is not a problem with respect tooxidation resistance if the first surface layer portion 2 and the secondsurface layer portion 3 are thick, the cost benefit will decrease sincethe proportion that the titanium alloy occupies with respect to theentire titanium composite material will increase. Therefore, thethickness of the first surface layer portion 2 and the second surfacelayer portion 3 with respect to the overall thickness of the titaniumcomposite material 1 is preferably 40% or less, respectively, and morepreferably is 30% or less.

The thickness of the first surface layer portion 2 and the secondsurface layer portion 3 of the titanium composite material 1 depend onthe thickness of a titanium alloy product constituting a package 6described later and on a working ratio in hot working performedthereafter. For example, when a titanium composite material 1 having athickness of 5 mm is produced by hot working the titanium material 5 forhot working having a thickness of 250 mm including the package 6constituted by titanium materials having a thickness of 1 mm, thethickness of the titanium alloy layer of each of the first surface layerportion 2 and the second surface layer portion 3 in the titaniumcomposite material 1 is about 20 μm, accounting for about 0.4% of theoverall thickness of the titanium composite material 1.

(Chemical Composition)

The oxidation of titanium takes an oxidation form so-called inwarddiffusion, in which oxygen diffuses in an oxidized film to bind totitanium on a surface. Therefore, if the diffusion of oxygen issuppressed, the oxidation is suppressed. For a titanium alloy, in thecase of improving an oxidation resistance at a high temperature of 600to 800° C., an alloying element such as Si and Nb is added.

The addition of Si causes silicon oxides to form in an outer layer tomake a barrier when exposed to an atmosphere at a high temperature,diffusion of oxygen to the inside of titanium is suppressed, and theoxidation resistance is improved. Further, while Ti is tetravalent, Nbis pentavalent. Therefore, Nb dissolving in an oxidized coating oftitanium decreases the concentration of oxygen holes in the oxidizedfilm, and the diffusion of oxygen in the oxidized film is suppressed.

The titanium composite material 1 according to the present invention maycontain various alloying elements described hereunder to increase theoxidation resistance of at least one of the first surface layer portion2 and the second surface layer portion 3 (at least a surface layerportion that contacts the external environment).

Si: 0.10 to 0.60%

Si has an action that improves oxidation resistance at a hightemperature of 600 to 800° C. If the Si content is less than 0.10%, thedegree of improvement in oxidation resistance will be small. On theother hand, if the Si content is more than 0.60%, the influence onoxidation resistance will be saturated and workability will noticeablydecline not only at room temperature but also at a high temperature.Hence, in a case where Si is to be contained, the content thereof ismade 0.10 to 0.60%. An Si content of 0.15% or more is preferable, and anSi content of 0.20% or more is more preferable, and the Si content ispreferably 0.50% or less, and more preferably is 0.40% or less.

Nb: 0.1 to 2.0%

Nb also has an action that improves oxidation resistance at a hightemperature. In order to improve oxidation resistance, the Nb content ismade 0.1% or more. On the other hand, even if the Nb content containedin the titanium alloy is more than 2.0%, the effect will be saturated,and this will also cause an increase in the alloy cost since Nb is anexpensive additional element. Hence, in a case where Nb is to becontained, the content thereof is made 0.1 to 2.0%. The Nb content ispreferably 0.3% or more, more preferably is 0.5% or more, and the Nbcontent is preferably 1.5% or less, and more preferably is 1.2% or less.

Ta: 0.3 to 1.0%

Ta also has an action that improves oxidation resistance at a hightemperature. In order to improve oxidation resistance, the Ta content ismade 0.3% or more. On the other hand, if the Ta content contained in thetitanium alloy is more than 1.0%, not only will this cause an increasein the alloy cost since Ta is an expensive additional element, butformation of β phase by a heat treatment temperature is also a concern.Hence, in a case where Ta is to be contained, the content thereof ismade 0.3 to 1.0%. The Ta content is preferably 0.4% or more, morepreferably is 0.5% or more, and the Ta content is preferably 0.9% orless, and more preferably is 0.8% or less.

Al: 0.3 to 1.5%

Al is also an element that improves oxidation resistance at a hightemperature. On the other hand, if Al is contained in a large amount,ductility at room temperature noticeably decreases. An oxidationresistance property is sufficiently exhibited if the Al content is 0.3%or more. Further, if the Al content is 1.5% or less, working performedas cold processing can be sufficiently ensured. Hence, in a case whereAl is to be contained, the content thereof is made 0.3 to 1.5%. The Alcontent is preferably 0.4% or more, more preferably is 0.5% or more, andthe Al content is preferably 1.2% or less.

Note that, although oxidation resistance is improved if any one of Si,Nb, Ta and Al is individually contained, high temperature oxidationresistance can be further improved by containing a combination of theseelements.

In addition to the above elements, one or more types of element selectedfrom Sn, Cu and Fe may be contained.

Sn: 0 to 1.5%

Sn is an α phase stabilizing element, and similarly to Cu, is an elementthat increases high temperature strength. However, if the Sn content ismore than 1.5%, the Sn inhibits twinning deformation and reducesworkability at room temperature. Therefore, in a case where Sn is to becontained, the content thereof is made 1.5% or less. The Sn content ispreferably 1.2% or less. When it is desired to obtain the aforementionedeffect, the Sn content is preferably 0.2% or more, and more preferablyis 0.4% or more.

Cu: 0 to 1.5%

Cu is an element that increases high temperature strength. Further,since Cu dissolves to a fixed degree in α phase, Cu does not form βphase even when used at a high temperature. However, if the Cu contentis more than 1.5%, the Cu may form β phase depending on the temperature.Therefore, in a case where Cu is to be contained, the content thereof ismade 1.5% or less. The Cu content is preferably 1.4% or less, and morepreferably is 1.2% or less. When it is desired to obtain theaforementioned effect, the Cu content is preferably 0.2% or more, andmore preferably is 0.4% or more.

Fe: 0 to 0.5%

Although Fe is a β phase stabilizing element, if Fe is contained in asmall amount, there is little formation of β phase, and the Fe will notsignificantly affect oxidation resistance. However, if the Fe content ismore than 0.5%, the formed amount of β phase is large, causing oxidationresistance to deteriorate. Therefore, in a case where Fe is to becontained, the content thereof is made 0.5% or less. Preferably the Fecontent is 0.4% or less, and more preferably is 0.3% or less.

If the total content of Sn, Cu and Fe is more than 2.5%, these elementswill decrease the workability at room temperature, and depending on thetemperature, 3 phase may be formed. Therefore, in a case where one ormore types of element selected from Sn, Cu and Fe is to be contained,preferably the total content thereof is not more than 2.5%.

The balance other than the above elements is Ti and impurities. Theimpurities can be contained in a range that does not inhibit the targetcharacteristics, and other impurities include Cr, V, Mn, Mo, and thelike as impurity elements that get mixed in mainly from scrap, andimpurities are allowed as long as the amount thereof together with C, N,O and H that are the common impurity elements is 5.0% or less.

(c) Case of Containing Alloying Elements Exhibiting Fatigue Resistance(Thickness)

If the thickness of a surface layer portion of the first surface layerportion 2 and the second surface layer portion 3 contacting the externalenvironment among the outer layers is too thin, fatigue resistance willnot be adequately obtained. Although the thickness of the first surfacelayer portion 2 and the second surface layer portion 3 changes dependingon the thickness of the material that is used for production and also ona working ratio thereafter, a sufficient effect is exerted if thethickness is 5 μm or more. Therefore, a thickness of at least one of thefirst surface layer portion 2 and the second surface layer portion 3 (atleast a surface layer portion that contacts the external environment) ispreferably 5 μm or more, and more preferably 10 μm or more. Further, thethickness of the first surface layer portion 2 and the second surfacelayer portion 3 with respect to the overall thickness of the titaniumcomposite material 1 is preferably 1% or more, respectively.

On the other hand, although there is not a problem with respect tofatigue resistance if the first surface layer portion 2 and the secondsurface layer portion 3 are thick, formability will decrease. Further,because the proportion that the titanium alloy occupies with respect tothe entire titanium composite material will increase, the cost benefitwill decrease. Therefore, the thickness of each of the first surfacelayer portion 2 and the second surface layer portion 3 is preferably 100μm or less, and more preferably is 50 μm or less. Further, the thicknessof the first surface layer portion 2 and the second surface layerportion 3 with respect to the overall thickness of the titaniumcomposite material 1 is preferably 20% or less, respectively, and morepreferably is 10% or less.

(Chemical Composition)

The titanium composite material 1 according to the present invention maycontain various alloying elements described hereunder to increase thefatigue resistance of at least one of the first surface layer portion 2and the second surface layer portion 3 (at least a surface layer portionthat contacts the external environment).

One or more types of element selected from Fe, Cr, Ni, Al and Zr: 0.08to 1.0% Because the origin of fatigue fracture is the surface of a sheetproduct, it is preferable to make the α-phase grain diameter 15 μm orless to obtain high fatigue resistance while maintaining formability.The α-phase grain diameter is more preferably made 10 μm or less, andfurther preferably is made 5 μm or less.

In order to make the α-phase grain diameter 15 μm or less and obtainhigh fatigue resistance, the total content of Fe, Cr, Ni, Al and Zr ismade 0.08% or more. On the other hand, if the total content of theseelements is more than 1.0%, in some cases the ductility such aselongation and formability significantly decreases. Therefore, the totalcontent of one or more types of element selected from Fe, Cr, Ni, Al andZr is made 0.08 to 1.0%.

The balance other than the above elements is Ti and impurities. Theimpurities can be contained in a range that does not inhibit the targetcharacteristics, and other impurities include Sn, Mo, V, Mn, Nb, Si, Cu,Co, Pd, Ru, Ta, Y, La, Ce, and the like as impurity elements that getmixed in mainly from scrap, and impurities are allowed as long as theamount thereof together with C, N, O and H that are the common impurityelements is 5.0% or less.

(Mechanical Properties)

The titanium composite material 1 has high fatigue strength while alsomaintaining excellent formability, with the fatigue strength ratio (10⁷cycles fatigue strength/tensile strength) being 0.65 or more. The higherthat the fatigue strength ratio is, the more excellent the material isin fatigue characteristics, and since this value is generally from 0.5to 0.6 for a titanium material, it can be said that if the value is 0.65or more the fatigue characteristics are superior in comparison to acommon titanium material, and if the value is 0.70 or more it can besaid that the fatigue characteristics are further superior.

In addition, in the titanium composite material 1, breaking elongationin a direction perpendicular to the rolling direction is 25% or more.Elongation has a significant influence on forming, and the greater theelongation is, the more excellent the formability that is exhibited.

(d) Case of Containing Alloying Elements Exhibiting HydrogenEmbrittlement Resistance (Thickness)

If the thickness of a surface layer portion of the first surface layerportion 2 and the second surface layer portion 3 contacting the externalenvironment among the outer layers is too thin, hydrogen absorptionresistance will not be adequately obtained. On the other hand, althoughthere is not a problem with respect to hydrogen absorption resistance ifthe titanium alloys in the first surface layer portion 2 and the secondsurface layer portion 3 are thick, since the proportion that thetitanium alloys in the first surface layer portion 2 and the secondsurface layer portion 3 occupy with respect to the entire material willincrease, the production cost will rise. Therefore, a thickness of atleast one of the first surface layer portion 2 and the second surfacelayer portion 3 with respect to the overall thickness of the titaniumcomposite material 1 (at least a surface layer portion that contacts theexternal environment) is made 2 to 20%.

The thickness of the first surface layer portion 2 and the secondsurface layer portion 3 of the titanium composite material 1 depend onthe thickness of a titanium alloy product constituting a package 6described later and on a working ratio in hot working performedthereafter. For example, when a titanium composite material 1 having athickness of 5 mm is produced by hot working the titanium material 5 forhot working having a thickness of 60 mm including the package 6constituted by titanium materials having a thickness of 5 mm, thethickness of the titanium alloy layer of each of the first surface layerportion 2 and the second surface layer portion 3 in the titaniumcomposite material 1 is about 0.4 mm, accounting for about 8% of theoverall thickness of the titanium composite material 1.

(Chemical Composition)

The titanium composite material 1 according to the present invention maycontain various alloying elements described hereunder to increase thehydrogen absorption resistance of at least one of the first surfacelayer portion 2 and the second surface layer portion 3 (at least asurface layer portion that contacts the external environment).

8.0<Mo equivalent<20.0

Where, Mo equivalent=Mo content (mass %)+V content (mass %)/1.5+Nbcontent (mass %)/3.6.

A layer that obtains hydrogen absorption resistance is a titanium alloylayer containing β stabilizing elements in a fixed range. The reason fordefining formation of the β phase is that, while the α phase of titaniumforms hydrides with even a very small hydrogen concentration of several10 ppm, the β phase of a titanium alloy can dissolve hydrogen ofapproximately 1000 ppm or more, and hence has a characteristic such thatit is difficult for embrittlement that is caused by hydrogen to occur.

In a case where eutectoid β stabilizing elements such as Fe and Cr arecontained, there is a risk of titanium and these elements forming acompound and causing embrittlement. However, in a case where, among theβ stabilizing elements, Mo, V and Nb are contained within a range thatsatisfies “8.0<Mo equivalent<20.0”, even if Fe and Cr or the like aresimultaneously present, embrittlement does not occur because the β phaseis stable and does not form a compound phase.

Here, the lower limit of the Mo equivalent is an alloy amount requiredto obtain a sufficient amount of β phase. The upper limit is set basedon the fact that a titanium alloy in which the amount of added alloyingelements is large is not suitable for use from a cost aspect since theprice thereof is high. Note that titanium alloy products used as thepackage 6 are not necessarily of β phase, and it suffices that β phasesurrounds α phase even if α phase precipitates in β phase.

An existing β-type titanium alloy can be utilized in the package 6described below, for the formation of alloy layers as the first surfacelayer portion 2 and the second surface layer portion 3. Examples thereofinclude Ti-15V-3Cr-3Al-3Sn, Ti-8V-3Al-6Cr-4Mo-4Zr (BetaC) andTi-11.5Mo-6Zr-4.5Sn (BetaIII). In the case of using such an existingβ-type titanium alloy in the package 6, such elements are allowed if theamount thereof together with the content of additional elements, such asCr, Sn, Al and Zr, that are other than the aforementioned elements is15% or less. These elements are elements which are contained foradjusting heat treatability, strength and cold workability in anexisting β-type titanium alloy, and do not reduce the Mo equivalentdefined in the present invention. Further, elements such as Si and Fe,for example, may also be contained.

The balance other than the above elements is Ti and impurities.Impurities can be contained in a range that does not inhibit the targetcharacteristics, and other impurities include Ta, Si, Mn, Cu, and thelike as impurity elements that get mixed in mainly from scrap, and theimpurities are allowed as long as the amount thereof together with C, N,Fe, O and H that are the common impurity elements is 5% or less.

(e) Case of Containing Alloying Elements Exhibiting Neutron BlockingProperties (Thickness)

If the thickness of a surface layer portion contacting the externalenvironment among the first surface layer portion 2 and the secondsurface layer portion 3 is too thin, a neutron shielding effect will notbe adequately obtained. On the other hand, in a case where the firstsurface layer portion 2 and the second surface layer portion 3 arethick, although a neutron shielding effect improves, since theproportion that the titanium alloy occupies with respect to the entirematerial increases, the production cost rises. Therefore, a thickness ofat least one of the first surface layer portion 2 and the second surfacelayer portion 3 with respect to the overall thickness of the titaniumcomposite material 1 (at least a surface layer portion that contacts theexternal environment) is made 5 to 40%.

The neutron shielding effect has a correlation with the thickness of thefirst surface layer portion 2 and the second surface layer portion 3with respect to the overall thickness of the titanium composite material1 described above, and the working ratio. For example, when a titaniumcomposite material 1 having a thickness of 10 mm is produced by hotworking the titanium material 5 for hot working having a thickness of100 mm including the package 6 having a thickness of 20 mm, thethickness of the titanium alloy layer of each of the first surface layerportion 2 and the second surface layer portion 3 in the titaniumcomposite material 1 is 2 mm, accounting for 20% (40% in total of bothportions) of the overall thickness of the titanium composite material 1.

Note that, in order to increase the thickness of the first surface layerportion 2 and the second surface layer portion 3, a sheet thickness ofalloy sheets bonded together when the package 6 is produced may beincreased. However, if the sheet thickness of the alloy sheets is toolarge, it is difficult to weld the alloy sheets to form the package 6.Therefore, the proportion of the alloy sheets may be increasedrelatively to the overall thickness of the titanium material 5 bydecreasing an original thickness of the titanium material 5 for hotworking.

(Chemical Composition)

The titanium composite material 1 according to the present inventioncontains an alloying element for providing a neutron shielding effect inthe first surface layer portion 2 and the second surface layer portion3. Hereunder, reasons for selecting an additional element, and reasonsfor limiting a range of an added amount of the additional element aredescribed in detail.

B: 0.1 to 3.0%

The natural abundance of ¹⁰B in B is 19.9%, and ¹⁰B has a largeabsorption cross section for thermal neutrons and a neutron shieldingeffect thereof is large. A neutron shielding effect is not adequatelyobtained if the B content is less than 0.1%, and if the B content ismore than 3.0% there is a risk of causing cracks and a deterioration inworkability during hot rolling.

In this case, it is possible to manufacture a titanium alloy containingB by adding B or a boride such as TiB₂ to titanium. Furthermore, ifmaterial containing ¹⁰B enriched boron (¹⁰B content is approximately 90%or more) such as H₃ ¹⁰BO₃, ¹⁰B₂O or ¹⁰B₄C is used, since the neutronshielding effect is large even if the B content is small, the titaniumalloy is extremely useful.

In the case of using H₃ ¹⁰BO₃, ¹⁰B₂O or ¹⁰B₄C, although H and O alsoconcentrate in the alloy layer, the H does not constitute a problemsince the H comes out from the material during a heat treatment such asvacuum annealing. And with respect to O and C, the material having the Ocontent of 0.4 percent by mass or less and the C content of 0.1 percentby mass or less which are not more than the respective upper limitscontained in a commercially pure titanium material can be manufacturedwithout a problem.

The balance other than the above elements is Ti and impurities. Theimpurities can be contained in a range that does not inhibit the targetcharacteristics, and other impurities include Cr, Ta, Al, V, Cr, Nb, Si,Sn, Mn, Mo, Cu and the like as impurity elements that get mixed inmainly from scrap, and impurities are allowed as long as the amountthereof together with C, N, Fe, O and H that are the common impurityelements is 5% or less.

(Applications)

In facilities in which radiation therapy such as particle radiotherapyand BNCT (boron neutron capture therapy) is performed, a polyethylenematerial is used in which the B content is 3.0 to 4.0 percent by massand the sheet thickness is 10 to 100 mm. Further, in facilities relatedto nuclear energy, stainless steel sheets in which the B content is 0.5to 1.5 percent by mass and the sheet thickness is 4.0 to 6.0 mm are usedin nuclear fuel storage racks. By using the titanium composite material1 in which the B content and thickness of the first surface layerportion 2 and the second surface layer portion 3 (thickness of aB-concentrated layer) are adjusted, it is possible to exertcharacteristics that are equal to or superior to the characteristics ofthe aforementioned materials.

1-3. Inner Layer Portion

(Chemical Composition)

The component of a pure titanium in the inner layer portion 4 of thetitanium composite material 1 depends on the component of a titaniumsponge used in the production of the titanium composite material 1, aswill be described hereunder. In the titanium composite material 1according to the present invention, among the pure titaniums specifiedin JIS, commercially pure titaniums of JIS Class 1, JIS Class 2, JISClass 3, or JIS Class 4 can be used. That is, commercially puretitaniums containing 0.1% or less of C, 0.015% or less of H, 0.4% orless of 0, 0.07% or less of N, and 0.5% or less of Fe, with the balancebeing Ti can be used.

When these commercially pure titaniums of JIS Classes 1 to 4 are used, atitanium material is obtained that has a sufficient workability, doesnot cause a crack or the like to occur, and is integrated with atitanium alloy-on the surface thereof after hot working. However, it isnoted that, because titanium is an active metal, if the average particlesize of a titanium sponge becomes a fine powder of 0.1 mm or less, asurface area per mass increases, and catch-up (concentration) of O isinevitable under real operation.

The O content in the inner layer portion of the titanium compositematerial can be adjusted depending on desired mechanical properties, andin a case where a high strength is needed, O may be contained up to itsmaximum of 0.4%. If the O content is more than 0.4%, a crack or the likeoccurs, there is a risk that the titanium material integrated with thetitanium alloy on the surface after hot working is not obtained. On theother hand, in a case where ductility is required rather than strength,it is preferable to decrease the O content, and the O content ispreferably 0.1% or less, and more preferably 0.05% or less.

(Porosity)

The titanium composite material 1 according to the present invention isproduced by hot working and cold working using the titanium material 5described later as a material. At such time, pores formed in the puretitanium portion in the titanium material 5 compressively bond whensubjected to the hot working and the cold working but are not completelyremoved, and some of the pores remain in the inner layer portion 4. Ifthe pores in this inner layer portion 4 are too many, mechanicalproperties (strength and ductility) for a bulk metal decrease, and theless the pores are, the more desirable it is.

However, in order to cause pores to compressively bond completely, alarge rolling reduction is necessary, the shape (thickness) of theproduced titanium composite material 1 is limited, and in addition, thiscan lead to a steep rise in producing cost. On the other hand, in a casewhere pores are contained to the extent that the titanium compositematerial 1 has sufficient mechanical properties (strength, ductility,and the like) to keep the structure of the titanium composite material1, the density of an interior titanium decreases, and therefore theweight reduction of the produced titanium composite material 1 can beexpected.

At such time, if the porosity in the inner layer portion 4 is 30% orless, the titanium composite material 1 is produced as the titaniumcomposite material 1 in which the inner layer portion 4 is integratedwith the first surface layer portion 2 and the second surface layerportion 3. In order to produce the titanium composite material 1efficiently, hot working and cold working are preferably performedexceeding a certain amount, and the porosity at this time is 10% orless.

As seen from the above, the porosity can be selected depending on uses,for example, the porosity is decreased in a case where mechanicalproperties as a bulk metal are important, and the porosity is increasedin a case where the weight reduction of a material is a high priority.The porosity in the inner layer portion 4 at such time is preferablymore than 0% and 30% or less, and more preferably more than 0% and 10%or less.

(Method for Calculating Porosity)

The proportion of the pores remaining in the inner layer portion 4 ofthe titanium composite material 1 (porosity) is calculated as follows.The titanium material is embedded in a resin such that the cross sectionof the titanium material can be observed, and thereafter a surface ofthe titanium material to be observed is buffed and subjected to mirrorfinish using diamond or an alumina suspension. Using this sample forobservation subjected to mirror finish, an optical micrograph of acenter of a sheet thickness is taken at 500× magnification. The areaproportion of pores observed on the taken optical micrograph ismeasured, and the measurement results of 20 micrographs are averaged andcalculated as the porosity. Although there is not a problem with respectto using a normal optical microscope as a microscope used in theobservation, it is preferable to use a differential interferencecontrast microscopy that is capable of polarized light observationbecause the differential interference contrast microscopy is capable ofperforming observation more clearly.

2. Material for Hot Working Made of Titanium Composite Material

FIG. 2 is an explanatory drawing illustrating the structure of atitanium material 5 for hot working that is a material for hot workingof the titanium composite material 1. The titanium composite material 1including a first surface layer portion 2 and a second surface layerportion 3 both consisting of a titanium alloy, and an inner layerportion 4 consisting of a pure titanium, and the titanium compositematerial 1 is produced by, for example, forming a package 6 asillustrated in FIG. 2 by creating an sealed entire circumference withtitanium alloy products having various characteristics, packing an innerportion of the package 6 with a titanium lump 7, reducing the pressureinside the package 6 to form the titanium material 5, and performing hotworking on this titanium material 5 as a material for hot working.Hereunder, each structure of the material is described in detail.

2-1. Titanium Lump

(Chemical Composition)

The titanium lump 7 supplied into the titanium material 5 for hotworking according to the present invention is a normal titanium lumpproduced by a conventional smelting process such as the Kroll process,and a commercially pure titanium that is equivalent to JIS Class 1, JISClass 2, JIS Class 3, or JIS Class 4 can be used as the component of thenormal titanium lump.

(Shape)

The titanium lump 7 contains one or more types selected from a titaniumsponge, a briquette obtained by compressing a titanium sponge, and acommercially pure titanium scrap. The size of the titanium lumps 7 ispreferably 30 mm or less in terms of average particle size. If theaverage particle size is larger than 30 mm, there is a problem withrespect to handling such as difficulty in handling the titanium lump 7when transferred and difficulty in putting the titanium lumps 7 into thetitanium material, and as a result, an operation efficiency becomespoor. Further, there is a possibility of decreasing a packing rate whenthe package 6 is packed with the titanium lump 7, and an averageparticle size larger than 30 mm decreases the density of the titaniumcomposite material 1 produced by the hot working and can lead to adecrease in characteristics such as ductility.

On the other hand, if the size of the titanium lump 7 is too small, dustconstitutes a problem when the package 6 is packed with the titaniumlumps 7, and there is not only a risk of hindering work but also a riskof the concentration of O during handling because a surface area permass increases. Therefore, the average particle size of the titaniumlumps 7 is preferably 0.1 mm or more, and more preferably 1 mm or more.

Note that, it is considered that a pure titanium powder subjected tomechanical milling (MM) treatment is used as an extremely fine powderthat has an average particle size of 0.1 mm or less. The MM treatment isa treatment in which a powder and hard balls are put in a pot andenclosed, and the powder is subjected to particle refining by vibratinga pot mill. The surface of the refined particle after the MM treatmentis in an active state, and therefore it is necessary to handle the fineparticle in an inert gas such that O and N in atmospheric air are notabsorbed when the pure titanium powder is collected from the pot.

Further, if a pure titanium having low concentrations of O and N issubjected to the MM treatment, since the pure titanium has a highductility, powders compressively bond, or the pure titaniumcompressively bonds to the hard balls or the surface of the pot.Therefore, a problem of a poor yield of the pure titanium powderobtained by performing the MM treatment arises. For such a reason,manufacturing a pure titanium powder by the MM treatment needs enormouslabors and expenses and unsuitable for volume production.

There is a method in which a titanium fine particle is produced from atitanium sponge by a hydrogenation-dehydrogenation method. However, thesurface area per mass increases, the O concentration is easy to increaseby surface oxidation, and therefore it is difficult to control amaterial quality. Consequently, the method according to the presentinvention in which a titanium sponge is used as it is, is excellent interms of quality and cost.

Note that in the case of using a titanium sponge as a briquette by pressmolding, a portion or all of the titanium sponge may be substituted witha scrap (pure titanium scrap) or a titanium powder.

2-2. Package

(Chemical Composition)

A titanium alloy having the alloy component described above is used suchthat the titanium alloy constitutes of a titanium alloy of the firstsurface layer portion 2 and the second surface layer portion 3 of thetitanium composite material 1 that is an end product.

(Shape)

Since the shape of the titanium alloy product used as the package 6depends on the shape of the titanium material 5 used as a material forhot working, the titanium alloy product has no special fixed form, and asheet product, a shell, or the like can be used. However, in order tomake the titanium composite material 1 produced by way of a producingprocess of hot working, cold working, annealing, or the like havegreater functionality by alloying an outer layer, and to provide anexcellent surface texture to the titanium composite material 1, thethickness of a titanium alloy product used for the package 6 isimportant.

If the titanium alloy product is thin and has a thickness of less than 1mm, the package 6 ruptures in the middle of the hot working as plasticdeformation is performed, a vacuum is lost, and the loss of vacuumcauses the oxidation of the titanium lump 7 inside. Further, theroughness of the titanium lump 7 packing inside the titanium material 5is transferred to the surface of the titanium material 5, and a largesurface roughness occurs on the surface of the titanium material 5during the hot working. These consequently have an adverse effect on themechanical properties of the produced titanium composite material 1 suchas surface texture and ductility and further on desired characteristics.

Further, also in a case where the surface defect does not occur duringthe hot working and the cold working, the thickness of a titanium alloyportion in the produced titanium composite material 1 is locallyreduced, and there is a possibility that sufficient characteristicscannot be exerted. Further, if the package 6 is excessively thin, thepackage 6 cannot support the weight of the titanium lump 7 packinginside, the titanium material 5 decreases in stiffness during retentionor working at a room temperature or as a hot processing, and thetitanium material 5 is deformed.

If the thickness of the titanium alloy product used for the package 6 is1 mm or more, the hot working can be performed without these problemsoccurring, and it is possible to produce the titanium composite material1 provided with an excellent surface texture and desiredcharacteristics. Note that it is more preferable to make the thicknessof the titanium alloy product 2 mm or more.

On the other hand, if the thickness of the titanium alloy product is toolarge, the proportion of the package 6 occupying with respect to theproduced titanium material 5 for hot working increases, the proportionof the titanium lump 7 occupying with respect to the titanium material 5relatively decreases, therefore a yield decreases, and the cost is high.

2-3. Titanium Material for Hot Working

Next, the titanium material 5 produced using the titanium lump 7 and thepackage 6 described above is described.

(Shape)

The shape of the titanium material 5 is not limited to a specific shapebut determined by the shape of the produced titanium composite material1. In the case of intending the production of a sheet product, atitanium material 5 having a rectangular-parallelepiped shape isproduced, and in the case of intending the production of a round bar, awire rod, or an extruded material, a titanium material 5 having apolygonal-prism shape such as a columnar shape and an octagonal prism isproduced. The size of the titanium material 5 is determined by the sizeof the product (thickness, width, length) and the amount of producing(weight).

(Inner Portion)

In the inner portion of the titanium material 5 the entire circumferenceof which is sealed with the package 6 is packed with the titanium lumps7. Since the titanium lumps 7 are massive grains, there are spaces(crevices) between the grains. To improve the handling ability of thetitanium lump 7 and to reduce these crevices, the titanium lumps 7 maybe put in the titanium material 5 after subjected to compressionmolding, in advance. If air remains in the crevices in the titaniummaterial 5, the titanium lumps 7 are oxidized or nitrided during heatingbefore the hot working, and the ductility of the produced titaniumcomposite material 1 decreases. Therefore, the pressure inside thetitanium material 5 is reduced to increase the degree of vacuum.

(Degree of Vacuum)

In order to prevent the titanium lumps 7 from being oxidized or nitridedin hot working, the degree of vacuum of the inner portion of thetitanium material 5 is made 10 Pa or less, and preferably 1 Pa or less.If the internal pressure of the titanium material 5 (absolute pressure)is more than 10 Pa, the titanium lumps 7 are oxidized or nitrided byresidual air. Although the lower limit of the degree of vacuum is notparticularly limited, making the degree of vacuum extremely small causesan increase in producing cost due to the improvement of airtightness ofa device, the enhancement of a vacuum pumping device, and the like, andtherefore, it is not necessary to make the degree of vacuum less than1×10−3 Pa.

(Welding)

As a method for welding the package 6, are welding such as tungsteninert gas welding and metal inert gas welding, electron beam welding,laser welding, or the like can be used, and the method is notparticularly limited. However, in order to prevent the surfaces of thetitanium lumps 7 and the package 6 from being oxidized or nitrided, awelding atmosphere is a vacuum atmosphere or an inert gas atmosphere. Ina case where the seams of the package 6 are welded last, the titaniummaterial 5 is welded with the titanium material 5 put into a container(chamber) of a vacuum atmosphere, it is preferable to keep the vacuum ofthe inner portion of the titanium material 5.

3. Method for Producing Titanium Composite Material

Next, a method for producing the titanium composite material 1 in whichhot working is performed on the titanium material 5 according to thepresent invention described above as a material for hot working isdescribed.

The titanium composite material (product) 1 is formed by hot working thetitanium material 5 as a material for hot working. A method of hotworking can be selected depending on the shape of the product.

In the case of producing a sheet product, a titanium material 5 having arectangular-parallelepiped shape (slab) is heated and subjected to hotrolling to be formed into a titanium sheet. As is the case with aconventional process, as required, after the hot rolling, an oxidizedlayer on the surface of the titanium sheet may be removed by pickling,and thereafter, the titanium sheet may be subjected to cold rolling andworked to be thinner.

In the case of producing a round bar or a wire rod, a titanium material5 having a cylindrical-column or polygonal shape (billet) is heated andsubjected to hot rolling or hot extrusion to be formed into a titaniumround bar or wire rod. Further, as required, similarly to a conventionalprocess, after the hot working, the oxidized layer of the titanium roundbar or wire rod may be removed by pickling, and thereafter, the titaniumround bar or wire rod may be subjected to cold rolling and worked to bethinner.

In addition, in the case of producing an extruded shape, a titaniummaterial 5 having a cylindrical-column or polygonal shape (billet) isheated and subjected to hot extrusion to be formed into a titaniumprofile varying in cross-sectional shape.

A heating temperature similar to that of a case of performing hotworking on a normal titanium slab or billet may be employed as theheating temperature before the hot working. Although differing dependingon the size of the titanium material 5 or a degree (working ratio) ofthe hot working, the heating temperature before the hot working ispreferably made 600° C. or more and 1200° C. or less. If the heatingtemperature is too low, the high temperature strength of the titaniummaterial 5 becomes too high and leads to a crack during hot working, andfurther, attachment of the titanium lump 7 and the package (titaniumalloy portion) 6 is insufficient. On the other hand, if the heatingtemperature is too high, the microstructure of the obtained titaniumcomposite material 1 becomes coarse, sufficient material characteristicsare not obtained, and further, the thickness of the package (titaniumalloy portion) 6 on the surface of titanium composite material 1 isreduced by oxidation. If the heating temperature is made 600 to 1200°C., the hot working can be performed without such a problem occurring.

The degree of working in the hot working, that is, a working ratio canbe selected for controlling the porosity of the inner portion of thetitanium composite material 1. The working ratio mentioned herein is aproportion (percentage) obtained by dividing the difference betweencross-sectional area of the titanium material 5 and the cross-sectionalarea the titanium composite material 1 after the hot working, by thecross-sectional area of the titanium material 5.

In a case where the working ratio is low, crevices between the titaniumlumps 7 in the inner portion of the titanium material 5 do notcompressively bond adequately and remain as pores after the hot working.The titanium composite material 1 including many such pores becomeslight by the included pores. However, because the pores are present inthe inner portion, the mechanical properties cannot exert adequately. Onthe other hand, as the working ratio increases, the porosity decreases,and the mechanical properties are improved. Consequently, in a casewhere importance is placed on the mechanical properties of the titaniumcomposite material 1 to be produced, the higher the working ratio is,the more preferable it is.

Specifically, when the working ratio is 90% or more, crevices in grainboundaries between the titanium lumps 7 in the inner portion of thetitanium material 5 can compressively bond adequately, and the pores intitanium composite material 1 can be reduced. Although the higher theworking ratio is, the more reliably the pores in the titanium compositematerial 1 are destroyed, and it is preferable, it is necessary toincrease the cross-sectional area of the titanium material 5, andfurther, it is necessary to repeat the hot working over and over again.As a result, there is a problem of a long production time or the like,and therefore the working ratio is preferably made 99.9% or less.

Hereunder, the present invention is more specifically described withreference to Examples, but the present invention is not limited to theseExamples.

Example 1 Example 1-1

Titanium sponge (JIS Class 1, Class 2, and Class 3, granularity=0.25 to19 mm) produced by the Kroll process and pure titanium scraps (JIS Class1, Class 2, and Class 3) were used as the titanium lump to be suppliedinto titanium materials. Further, using Ti-0.06Pd alloy sheet products(thickness was 0.5 to 20 mm), rectangular parallelepipeds having athickness of 50 to 100 mm, a width of 100 mm, and a length of 120 mmwere fabricated as the packages.

When manufacturing the titanium material, first, five titanium sheetswere preassembled into a box shape, and thereafter, a titanium spongewas supplied into the box shape, and an opening portion of thepreassembled box is covered with a titanium sheet. For some titaniummaterials, titanium sponges (sponge briquettes) formed into a briquetteshape or briquettes obtained by mixing a titanium sponge and a puretitanium scrap were used instead of the titanium sponges. Thepreassembled titanium material was put inside a vacuum chamber, and thepressure of the vacuum chamber was reduced to a predetermined pressure(vacuum), and thereafter seams of the entire circumference of thepackage were welded and sealed by an electron beam. The degree of vacuuminside the chamber at that time was made 8.7×10⁻³ to 7.6×10−2 Pa, asshown in Table 2.

In each of some titanium materials (Test Nos. 16 and 17 in Table 2), onesheet of package 1 with a hole opened in the center of the sheet and atitanium pipe having an inner diameter of 6 mm TIG-welded to the holewas prepared, and the titanium material was temporarily assembled suchthat the one sheet of package is made a rear end face when subjected torolling.

Thereafter, the entire circumference of the temporarily assembledtitanium material was welded by an electron beam, and thereafter, thepressure inside the titanium material was reduced through the titaniumpipe to a predetermined degree of vacuum (6.9×10⁻¹ to 1.2 Pa), and afterthe pressure reduction, the degree of vacuum inside the titaniummaterial was kept by clamping the titanium pipe.

By the processes described above, a package the entire circumference ofwhich is sealed with titanium-alloy made sheets was formed, the innerportion of the package was packed with titanium lumps, and the pressureof the inner portion of the package was reduced to the predetermineddegree of vacuum.

The fabricated titanium material was heated in an air atmosphere to 850°C. and thereafter subjected to hot rolling to be formed into ahot-rolled sheet having a thickness of 5 mm. Thereafter, both surfacesof the titanium material were subjected to descaling treatment byperforming shotblast and using nitric-hydrofluoric acid. In addition,the titanium material was subjected to cold rolling to be formed into atitanium sheet having a thickness of 1 mm, subjected to heat treatmentin which the titanium material was heated to 600 to 750° C. and retainedfor 240 minutes in vacuum or in an inert gas atmosphere, as annealingtreatment, and thereby a specimen according to the present invention wasfabricated.

From this hot-rolled sheet, a test specimen of 1 mm×30 mm×40 mm(thickness×width×length) was cut out, a cut surface of the test specimenand a surface of the test specimen to which no corrosion resistanttitanium alloy sheet was stuck were covered with anti-corrosion tapessuch that the cut surface and the surface would not be exposed to acorrosive environment, thereafter, the test specimen was immersed in 3%boiling hydrochloric acid (pH≈0 at normal temperature) for 96 hours, andthereafter, a corrosion rate was calculated from a change in weightbefore and after a corrosion test.

Further, the produced titanium composite material was embedded in aresin so as to be subjected to cross section observation, the producedtitanium composite material was polished and etched and thereafterobserved under an optical microscope, and the thickness of a surfacelayer portion titanium alloy layer was measured. This measured thicknessof the surface layer portion titanium alloy layer was divided by theoverall thickness of the titanium composite material to be calculated asa surface layer portion ratio.

In order to calculate a proportion of pores remaining in a pure titaniumportion of the titanium composite material (hereinafter referred to asporosity), a sample was embedded in a resin such that the cross sectionof the sample can be observed, thereafter polished and subjected tomirror finish, and thereafter, optical micrographs were taken at 500×magnification. The area proportion of pores were calculated from thetaken optical micrographs, the measurement results of five micrographswere averaged and calculated as the porosity. The surface texture of theproduced titanium composite material was evaluated in terms of whether aflaw is present or absent in observation with visual check.

For comparison with the titanium composite material according to thepresent invention, commercially pure titaniums (JIS Classes 1 to 3) anda 1 mm sheet product of a commercially corrosion resistant titaniumalloy (Ti-0.06% Pd, ASTM Gr.17) were used to perform the corrosion testdescribed in the foregoing.

The results of the above are collectively shown in Table 2.

TABLE 2 Titanium material for hot working Titanium Titanium compositeMaterial used as Titanium material material inner portion InteriorPackage material degree of Outer layer Test of package pure thicknessthickness vacuum thickness No. Kind Dimensions titanium (mm) (mm) (Pa)(μm) 1 — — — — — — * 2 — — — — — — * 3 — — — — — — * 4 — — — — — — * 5Titanium 1.0~19 mm JIS Class 1 20 50 8.9 × 10⁻³ 405 sponge 6 Titanium1.0~19 mm JIS Class 1 20 60 8.9 × 10⁻³ 325 sponge 7 Titanium 1.0~19 mmJIS Class 1 10.2 75 8.7 × 10⁻³ 128 sponge 8 Titanium 1.0~19 mm JIS Class2 10.2 75 8.7 × 10⁻³ 135 sponge 9 Titanium 1.0~19 mm JIS Class 3 10.2 758.7 × 10⁻³ 142 sponge 10 Titanium 1.0~19 mm JIS Class 1 8.0 75 1.2 ×10⁻²  99 sponge 11 Titanium 1.0~19 mm JIS Class 1 2.5 75 8.7 × 10⁻³  25sponge 12 Titanium 1.0~19 mm JIS Class 1 1.5 75 7.6 × 10⁻²  12 sponge 13Titanium 1.0~19 mm JIS Class 1 1.1 75 8.7 × 10⁻³    6.7 sponge 14Titanium 1.0~19 mm JIS Class 1 1.1 100 8.7 × 10⁻³    3.0 sponge 15Titanium 1.0~19 mm JIS Class 1 1.1 100 8.9 × 10⁻³    0.9 * sponge 16Titanium 1.0~19 mm JIS Class 1 10.2 75 6.9 × 10⁻¹ 128 sponge 17 Titanium1.0~19 mm JIS Class 1 10.2 75 1.2 128 sponge 18 Sponge 1.0~19 mm JISClass 1 10.2 75 8.7 × 10⁻³ 125 briquette 19 Scrap- 1.0~19 mm JIS Class 110.2 75 8.7 × 10⁻³ 129 including sponge briquette Titanium compositematerial Corrosion Surface rate layer (mm/y) portion 3% boiling Testratio Porosity hydrochloric No. (%) (%) acid Remarks 1 — * 0 4.12Commercially material Comparative (JIS Class 1) Example 2 — * 0 4.26Commercially material (JIS Class 2) 3 — * 0 4.31 Commercially material(JIS Class 3) 4 100 *  0 0.37 Commercially material (Ti—0.06Pd, ASTMGr17) 5   40.5 * 0.1 0.36 Ti—0.06Pd (ASTM Gr17) was used as package 632.5 0.2 0.37 Ti—0.06Pd (ASTM Gr17) Inventive was used as packageExample 7 12.8 0.2 0.36 Ti—0.06Pd (ASTM Gr17) was used as package 8 13.50.2 0.37 Ti—0.06Pd (ASTM Gr17) was used as package 9 14.2 0.2 0.37Ti—0.06Pd (ASTM Gr17) was used as package 10  9.9 0.2 0.35 Ti—0.06Pd(ASTM Gr17) was used as package 11  2.5 0.2 0.37 Ti—0.06Pd (ASTM Gr17)was used as package 12  1.2 0.3 0.36 Ti—0.06Pd (ASTM Gr17) was used aspackage 13  0.7 0.3 0.37 Ti—0.06Pd (ASTM Gr17) was used as package 14 0.3 0.2 0.37 Ti—0.06Pd (ASTM Gr17) was used as package 15  0.1 0.2 2.58Ti—0.06Pd (ASTM Gr17) Comp. Ex. was used as package 16 12.8 0.5 0.36Ti—0.06Pd (ASTM Gr17) Inventive was used as package Example 17 12.8 0.60.36 Ti—0.06Pd (ASTM Gr17) was used as package 18 12.5 0.2 0.35Ti—0.06Pd (ASTM Gr17) was used as package Sponge briquette was used ininner portion of package 19 12.9 0.2 0.37 Ti—0.06Pd (ASTM Gr17) was usedas package Sponge briquette containing pure titanium scrap was used ininner portion of package The mark “*” indicates that the value fell outof the definition according to the present invention.

Test Nos. 1 to 4 being Comparative Examples were the commercially puretitanium materials (JIS Classes 1 to 3) and the commercially corrosionresistant titanium material (Ti-0.06Pd, ASTM Gr.17) produced by way ofmelting, decomposing, and forging processes, respectively, and theseresults serve as benchmarks to evaluate the performance of the titaniumcomposite material of the present invention described later.

Test Nos. 5 to 14 and 16 to 19 being Inventive Example of the presentinvention all exhibited corrosion resistances that were superior tothose of the commercially pure titanium materials produced by way ofmelting, decomposing, and forging process shown as test Nos. 1 to 3 inTable 2 described in the foregoing, and had corrosion resistances thatwere equivalent to that of the commercially corrosion resistant titaniummaterial produced by way of melting, decomposing, and forging processesshown as test No. 4.

However, although not having a problem with respect to corrosion rate,test No. 5 had a large surface layer portion contain, the proportionthat the titanium alloy portion accounts for was relatively large, andthe material cost increased.

Test No. 15 had a corrosion resistance better than that of the puretitanium because the thickness of the surface layer portion was small,but the result of corrosion resistance was inferior to that of thecorrosion resistant titanium alloy.

Test Nos. 18 and 19 were titanium composite materials produced using asponge briquette or a pure-titanium-scrap-containing sponge briquette inwhich a pure titanium scrap is utilized in a portion of the titaniumsponge, as the pure titanium in the inner portion of the titaniummaterial. Test Nos. 18 and 19 had excellent corrosion resistancesequivalent to the corrosion resistance of the corrosion resistanttitanium alloy similarly to a case where a titanium sponge was used asthe inner portion.

Example 1-2

Titanium sponge (JIS Class 1, granularity=0.25 mm or more and 19 mm orless) produced by the Kroll process was used as the titanium lumps to besupplied into titanium materials. Further, using a titanium alloycontaining predetermined components (thickness was 10 mm), rectangularparallelepipeds having a thickness of 75 mm, a width of 100 mm, and alength of 120 mm were fabricated as the package.

When manufacturing the titanium material, first, five titanium sheetswere preassembled into a box shape, and thereafter, a titanium spongewas supplied into the box shape, and an opening portion of thepreassembled box is covered with a titanium sheet. The preassembledtitanium material was put inside a vacuum chamber, and the pressure ofthe vacuum chamber was reduced to 8.7×10⁻³ Pa, and thereafter seams ofthe entire circumference of the package were welded and sealed by anelectron beam.

By the processes described above, a package the entire circumference ofwhich is sealed with titanium-alloy made sheet products was formed, theinner portion of the package was packed with a titanium sponge, and thepressure of the inner portion of the package was reduced to thepredetermined degree of vacuum.

The fabricated titanium material was heated in an air atmosphere to 850°C. and thereafter subjected to hot rolling to be formed into ahot-rolled sheet having a thickness of 5 mm. From this specimen, a testspecimen of 5 mm×30 mm×40 mm (thickness×width×length) was cut out, andthereafter, the evaluation similar to Example 1-1 was performed.

For comparison with the titanium composite material according to thepresent invention, a 5 mm sheet product of a commercially pure titanium(JIS Class 1) and a 5 mm sheet product of a commercially corrosionresistant titanium alloy (Ti-0.06% Pd, ASTM Gr. 17) were used to performthe corrosion test described in the foregoing.

These results are collectively shown in Table 3.

TABLE 3 Titanium material for hot working Chemical composition ofpackage Titanium (by mass %, balance: Ti and impurities) Material usedas Interior Package material Platinum Rare Test inner portion of packagepure thickness thickness group earth No. Kind Dimensions titanium (mm)(mm) element elements Co Ni 20 — — — — — — — — — 21 — — — — — Pd: 0.06 —<0.01  — 22 — — — — — Pd: 0.06 — 0.31 — 23 — — — — — Pd: 0.14 — — — 24Titanium sponge 1.0~19 mm JIS Class 1 10.2 75 Pd: 0.25 — — — 25 Titaniumsponge 1.0~19 mm JIS Class 1 10.2 75 Pd: 0.14 — — — 26 Titanium sponge1.0~19 mm JIS Class 1 10.2 75 Pd: 0.06 — — — 27 Titanium sponge 1.0~19mm JIS Class 1 10.2 75 Pd: 0.02 — — — 28 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Pd: 0.01, — — — Ru: 0.03 29 Titanium sponge 1.0~19 mmJIS Class 1 10.2 75 Pd: 0.06 — 0.30 — 30 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Pd: 0.02 — 0.80 — 31 Titanium sponge 1.0~19 mm JIS Class1 10.2 75 Pd: 0.02 Y: 0.25 — — 32 Titanium sponge 1.0~19 mm JIS Class 110.2 75 Pd: 0.02 Y: 0.19 — — 33 Titanium sponge 1.0~19 mm JIS Class 110.2 75 Pd: 0.01 Y: 0.02 — — 34 Titanium sponge 1.0~19 mm JIS Class 110.2 75 Pd: 0.02 Y: 0.003 — — 35 Titanium sponge 1.0~19 mm JIS Class 110.2 75 Pd: 0.03 Dy: 0.10 — — 36 Titanium sponge 1.0~19 mm JIS Class 110.2 75 Pd: 0.03 La: 0.08 — — 37 Titanium sponge 1.0~19 mm JIS Class 110.2 75 Pd: 0.03 Didymium: 0.04 — — 38 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Pd: 0.03 Pr: 0.04 — — 39 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Pd: 0.02 Ce: 0.09 — — 40 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Pd: 0.02 Mm: 0.05 — — 41 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Ru: 0.04 Y: 0.02 — — 42 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Pd: 0.02 Nd: 0.05 0.21 — 43 Titanium sponge 1.0~19 mmJIS Class 1 10.2 75 Pd: 0.01 Sm: 0.06 0.30 — 44 Titanium sponge 1.0~19mm JIS Class 1 10.2 75 Ru: 0.05 — — 0.50 45 Titanium sponge 1.0~19 mmJIS Class 1 10.2 75 Ru: 0.05 — — 0.20 46 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Ru: 0.04 Y: 0.02 — 0.30 47 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Pd: 0.02 — 0.30 0.19 48 Titanium sponge 1.0~19 mm JISClass 1 10.2 75 Pd: 0.02 Y: 0.02 0.20 0.20 Titanium composite materialSurface Corrosion rate Outer layer (mm/y) layer portion 3% boiling Testthickness ratio Porosity hydrochloric No. (μm) (%) (%) acid Remarks 20— * — * 0 * 4.15 Commercially material Comparative (JIS Class 1) Example21 — * 100 *  0 * 0.36 Commercially material (ASTM Gr17) 22 — * 100 * 0 * 0.22 Commercially material (ASTM Gr19) 23 — * 100 *  0 * 0.04Commercially material (ASTM Gr7) 24 680 13.8 0.1 0.03 Inventive 25 65013.2 0.1 0.05 Example 26 600 12.2 0.1 0.38 27 590 12.0 0.1 0.70 28 63012.8 0.1 0.40 29 650 13.2 0.1 0.22 30 690 14.0 0.1 0.16 31 750 15.2 0.20.42 32 750 15.2 0.1 0.38 33 610 12.4 0.1 0.29 34 600 12.2 0.1 0.30 35610 12.4 0.1 0.23 36 615 12.5 0.1 0.25 37 610 12.4 0.1 0.24 38 600 12.20.1 0.23 39 620 12.6 0.1 0.24 40 615 12.5 0.1 0.25 41 620 12.6 0.1 0.2942 660 13.4 0.1 0.20 43 655 13.3 0.1 0.22 44 590 12.0 0.1 0.32 45 59512.1 0.1 0.43 46 610 12.4 0.1 0.31 47 630 12.8 0.2 0.25 48 700 14.2 0.20.19 The mark “*” indicates that the value fell out of the definitionaccording to the present invention.

Test Nos. 20 to 23 being Comparative Examples, commercially puretitanium materials (JIS Class 1) produced by way of melting,decomposing, and forging processes were commercially corrosion resistanttitanium materials produced by way of melting, decomposing, and forgingprocesses, and these results serve as benchmarks to evaluate theperformance of the titanium composite material according to the presentinvention described later.

Test Nos. 24 to 48 being Inventive Example of the present invention allexhibited corrosion resistances that were as excellent as those ofcommercially corrosion resistant titanium materials produced by way ofmelting, decomposing, and forging processes shown as test Nos. 21 to 23,and had corrosion resistances that were superior to that of acommercially pure titanium material produced by way of melting,decomposing, and forging processes shown as test No. 20.

Test Nos. 24 to 27 were imparted excellent corrosion resistances bycontaining Pd being a platinum group element in the surface layerportion titanium alloy.

Test No. 28 was imparted an excellent corrosion resistance by containingPd and Ru being platinum group elements in the surface layer portiontitanium alloy.

Test Nos. 29 and 30 were imparted excellent corrosion resistances bycontaining Pd being a platinum group element, as well as Co, in thesurface layer portion titanium alloy.

Test Nos. 31 to 41 were imparted excellent corrosion resistances bycontaining Pd or Ru being a platinum group element, as well as Y, Dy,La, didymium, Pr, Ce, or Mm being rare earth elements, in the surfacelayer portion titanium alloy.

Test Nos. 42 and 43 were imparted excellent corrosion resistances bycontaining Pd being a platinum group element, as well as Nd and Sm beingrare earth elements, and further Co, in the surface layer portiontitanium alloy.

Test Nos. 44 and 45 were imparted excellent corrosion resistances bycontaining Ru being a platinum group element, as well as Ni, in thesurface layer portion titanium alloy.

Test No. 46 was imparted an excellent corrosion resistance by containingPd being a platinum group element, as well as Y being a rare earthelement, and further Ni, in the surface layer portion titanium alloy.

Test No. 47 was imparted an excellent corrosion resistance by adding Pdbeing a platinum group element, as well as Co and Ni in the surfacelayer portion titanium alloy.

In addition, test No. 48 was imparted an excellent corrosion resistanceby adding Pd being a platinum group element, as well as Y being a rareearth element, and further Co and Ni, in the surface layer portiontitanium alloy.

Example 1-3

Titanium sponge (JIS Class 1, granularity=0.25 mm or more and 19 mm orless) produced by the Kroll process was used as the titanium lumps to besupplied into titanium materials. Further, using Ti-0.06Pd alloy sheetproducts, rectangular parallelepipeds having a thickness of 25 to 75 mm,a width of 100 mm, and a length of 120 mm were manufactured as thepackages.

When manufacturing the titanium material, first, five titanium sheetswere preassembled into a box shape, and thereafter, a titanium spongewas supplied into the box shape, and an opening portion of thepreassembled box is covered with a titanium sheet. The preassembledtitanium material was put inside a vacuum chamber, and the pressure ofthe vacuum chamber was reduced to 8.7×10⁻³ Pa, and thereafter seams ofthe entire circumference of the package were welded and sealed by anelectron beam.

By the processes described above, a package the entire circumference ofwhich is sealed with titanium-alloy made sheets was formed, the innerportion of the package was packed with a titanium sponge, and thepressure of the inner portion of the package was reduced to thepredetermined degree of vacuum.

The manufactured titanium material was heated in an air atmosphere to850° C. and thereafter subjected to hot rolling to be formed into ahot-rolled sheet having a thickness of 20 mm. The obtained hot-rolledsheet was subjected to vacuum annealing at 725° C., thereafter subjectedto shotblast working, and finished by pickling using nitric-hydrofluoricacid to be formed into a titanium composite material. From thisspecimen, a test specimen of 20 mm×50 mm×50 mm (thickness×width×length)was cut out, and thereafter, the evaluation similar to Examples 1-1 and1-2 was performed.

These results are collectively shown in Table 4.

TABLE 4 Titanium composite Titanium material for hot working materialMaterial used as Titanium Outer inner portion Interior Package materiallayer Test of package pure thickness thickness thickness No. KindDimensions titanium (mm) (mm) (μm) 49 — — — — — — * 50 — — — — — — * 51Titanium sponge 1.0~19 mm JIS Class 1 1.1 25 970 52 Titanium sponge1.0~19 mm JIS Class 1 1.1 30 800 53 Titanium sponge 1.0~19 mm JIS Class1 1.1 35 790 54 Titanium sponge 1.0~19 mm JIS Class 1 1.1 50 520 55Titanium sponge 1.0~19 mm JIS Class 1 1.1 75 300 Titanium compositematerial Surface Corrosion rate layer (mm/y) portion 3% boiling Testratio Porosity hydrochloric No. (%) (%) acid Remarks 49 — * 0 * 4.15Commercially material Comparative (JIS Class 1) Example 50 100 *  0 *0.36 Commercially material (ASTM Gr17, Ti—0.06Pd) 51 4.9 22.5  0.38Ti—0.06Pd (ASTM Gr17) Inventive was used as package Example 52 4.0 9.90.36 Ti—0.06Pd (ASTM Gr17) was used as package 53 4.0 2.1 0.37 Ti—0.06Pd(ASTM Gr17) was used as package 54 2.6 0.9 0.36 Ti—0.06Pd (ASTM Gr17)was used as package 55 1.5 0.5 0.36 Ti—0.06Pd (ASTM Gr17) was used aspackage The mark “*” indicates that the value fell out of the definitionaccording to the present invention.

Test Nos. 51 to 55 being Inventive Example of the present invention allexhibited corrosion resistances that were superior to that of thecommercially pure titanium material produced by way of melting,decomposing, and forging process shown as test No. 49, and had corrosionresistances that were equivalent to that of the commercially corrosionresistant titanium material produced by way of melting, decomposing, andforging processes shown as test No. 50.

Example 2 Example 2-1

In each of test Nos. 1 to 18 shown in Table 5, the square package 6having 250 mm×1000 mm×4500 mm (thickness×width×length) and consisting oftitanium alloy sheets containing at least one type of Si, Nb, Ta, and Alwas manufactured, and thereafter the titanium lumps 7 consisting of thecommercially pure titanium (one or more types of material selected frombriquette, scrap, and titanium sponge) were supplied in the innerportion of the package 6, the package 6 was enclosed under a vacuumatmosphere at about 8×10⁻² Pa to be formed into the titanium material 5,and the titanium material 5 was used as a material for hot rolling.

Thereafter, this titanium material 5 was heated to 820° C. and subjectedto hot rolling to have a thickness of 5 mm, and thereafter, bothsurfaces of the titanium material 5 were subjected to descalingtreatment by performing shotblast and using nitric-hydrofluoric acid.

In addition, the titanium material 5 was subjected to cold rolling to beformed into a titanium composite material 1 having a thickness of 1 mm,and subjected to heat treatment in which the titanium material washeated to 600 to 750° C. and retained for 240 minutes in vacuum or in aninert gas atmosphere, as annealing treatment.

From these test specimens, 20 mm×20 mm test specimens were taken, thesurfaces and the end portions of the test specimens were polished with#400 sandpaper, and thereafter, the test specimens were exposed to theatmospheric air at temperatures of 700 and 750° C. for 200 hours foreach of the temperatures, a change in weight of each of the testspecimens before and after the test was measured, and an oxidationweight gain per unit cross-sectional area was calculated.

TABLE 5 Titanium material for hot working Titanium material Materialused as Interior Package degree of Chemical composition of package Testinner portion pure thickness vacuum (mass %) No. of package titanium(mm) (Pa) Si Nb Al Ta 1 — JIS Class 2 — 8 × 10⁻² — — — — 2 Briquette JISClass 1 15.0 8 × 10⁻² 0.31 — — — 3 Briquette JIS Class 2 17.5 8 × 10⁻²0.45 — — — 4 Briquette + titanium JIS Class 3 14.0 8 × 10⁻² 0.22 — — —sponge 5 Briquette + scrap JIS Class 2 12.0 8 × 10⁻² — 0.90 — — 6Scrap + titanium JIS Class 2 14.0 8 × 10⁻² — — — 0.55 sponge 7Briquette + titanium JIS Class 2 22.0 8 × 10⁻² — — 1.20 — sponge 8Briquette + titanium JIS Class 2 19.5 8 × 10⁻² 0.25 0.35 — — sponge 9Briquette + titanium JIS Class 2 16.0 8 × 10⁻² 0.31 0.44 — 0.44 sponge10 Briquette + titanium JIS Class 2 16.5 8 × 10⁻² 0.35 — 0.90 — sponge11 Briquette + titanium JIS Class 2 30.0 8 × 10⁻² 0.35 0.35 — 0.85sponge 12 Briquette + titanium JIS Class 2 18.0 8 × 10⁻² — 0.80 0.29 —sponge 13 Briquette + titanium JIS Class 2 15.5 8 × 10⁻² — — 0.81 0.35sponge + scrap 14 Briquette + titanium JIS Class 2 14.0 8 × 10⁻² 0.230.45 — 0.31 sponge + scrap 15 Briquette + titanium JIS Class 2 15.0 8 ×10⁻² — 0.80 0.29 0.40 sponge + scrap 16 Briquette + titanium JIS Class 215.5 8 × 10⁻² 0.45 0.20 0.50 — sponge + scrap 17 Briquette + titaniumJIS Class 2 16.0 8 × 10⁻² 0.20 — 0.30 0.55 sponge + scrap 18 BriquetteJIS Class 2 18.0 8 × 10⁻² 0.20 0.30 0.30 0.35 Titanium compositematerial Surface Outer layer Oxidation layer portion weight gain Testthickness ratio Porosity (g/m²) No. (μm) (%) (%) 700° C. 750° C.Producibility 1 — * — * 0.02 45 130 Good Comp. Ex. 2 51 5.1 0.04 19 54Good Inventive 3 63 6.3 0.01 18 55 Good Example 4 48 4.8 0.09 19 53 Good5 39 3.9 0.04 21 63 Good 6 48 4.8 0.07 23 68 Good 7 80 8.0 0.05 25 70Good 8 70 7.0 0.09 15 43 Good 9 56 5.6 0.08 14 42 Good 10 58 5.8 0.04 1849 Good 11 105 10.5 0.03 23 59 Good 12 65 6.5 0.01 18 48 Good 13 54 5.40.01 21 51 Good 14 48 4.8 0.10 16 43 Good 15 52 5.2 0.30 17 45 Good 1656 5.6 0.05 14 40 Good 17 57 5.7 0.08 18 42 Good 18 63 6.3 0.32 15 41Good The mark “*” indicates that the value fell out of the definitionaccording to the present invention.

In Test No. 1 being a Comparative Example, the inner layer portion 4consisted of the commercially pure titanium of JIS Class 2, and thefirst surface layer portion 2 and the second surface layer portion 3were not included. Therefore, the oxidation weight gain in the heatingat 700° C. for 200 hours was 40 g/m² or more, the oxidation weight gainin the heating at 750° C. for 200 hours was 100 g/m² or more, and thesewere very large.

In Test No. 2, the inner layer portion 4 consisted of the commerciallypure titanium of JIS Class 1, the first surface layer portion 2 and thesecond surface layer portion 3 contained Si and had a thickness of 5 μmor more, and this thickness was a sufficient thickness. Therefore, theoxidation weight gain in the heating at 700° C. for 200 hours was 25g/m² or less, the oxidation weight gain in the heating at 750° C. for200 hours was 70 g/m² or less, and test No. 2 exhibited an excellentoxidation resistance. Further, the porosity was less than 1%, and themechanical nature was good.

In Test No. 3, the inner layer portion 4 consisted of the commerciallypure titanium of JIS Class 2, the first surface layer portion 2 and thesecond surface layer portion 3 contained Si and had a thickness of 5 μmor more, and this thickness was a sufficient thickness. Therefore, theoxidation weight gain in the heating at 700° C. for 200 hours was 25g/m² or less, the oxidation weight gain in the heating at 750° C. for200 hours was 70 g/m² or less, and test No. 2 exhibited an excellentoxidation resistance. Further, the porosity was less than 1%, and themechanical nature was good.

In Test No. 4, the inner layer portion 4 consisted of the commerciallypure titanium of JIS Class 3, the first surface layer portion 2 and thesecond surface layer portion 3 contained Si and had a thickness of 5 μmor more, and this thickness was a sufficient thickness. Therefore, theoxidation weight gain in the heating at 700° C. for 200 hours was 25g/m² or less, the oxidation weight gain in the heating at 750° C. for200 hours was 70 g/m² or less, and test No. 2 exhibited an excellentoxidation resistance. Further, the porosity was less than 1%, and themechanical nature was good.

In Test Nos. 5 to 18, the inner layer portion 4 consisted of thecommercially pure titanium of JIS Class 2, the first surface layerportion 2 and the second surface layer portion 3 contained one or moretypes of element selected from Si, Nb, Ta, and Al, and had a thicknessof 5 μm or more, and this thickness was a sufficient thickness.Therefore, the oxidation weight gain in the heating at 700° C. for 200hours was 25 g/m² or less, the oxidation weight gain in the heating at750° C. for 200 hours was 70 g/m² or less, and test No. 2 exhibited anexcellent oxidation resistance. Further, the porosity was less than 1%,and the mechanical nature was good.

Example 2-2

In each of test Nos. 19 and 20 shown in Table 6, the package 6 having 50mm×1000 mm×4000 mm (thickness×width×length) and consisting of titaniumalloy sheets containing Nb was manufactured, thereafter the titaniumlumps 7 consisting of the commercially pure titanium (briquette andtitanium sponge) was supplied in the inner portion of the package 6, thepackage 6 was enclosed under a vacuum atmosphere at about 8×10⁻² Pa tobe formed into the titanium material 5, and the titanium material 5 wasused as a material for hot rolling.

This titanium material 5 was heated to 820° C. and subjected to hotrolling to have a thickness of 20 mm, and thereafter, both surfaces ofthe titanium material 5 were subjected to descaling treatment byperforming shotblast and using nitric-hydrofluoric acid. In addition,the titanium material 5 was subjected to heat treatment in which thetitanium material was heated to 600 to 700° C. and retained for 240minutes in a vacuum or in an inert gas atmosphere, as annealingtreatment.

TABLE 6 Titanium material for hot working Titanium material Materialused as Interior Package degree of Chemical composition of package Testinner portion pure thickness vacuum (mass %) No. of package titanium(mm) (Pa) Si Nb Al Ta 19 Briquette + titanium JIS Class 2 18.0 8 × 10⁻²— 0.85 — — sponge 20 Briquette + titanium JIS Class 3 18.0 8 × 10⁻² —1.85 — — sponge Titanium composite material Surface Outer layerOxidation layer portion weight gain Test thickness ratio Porosity (g/m²)No. (μm) (%) (%) 700° C. 750° C. Producibility 19 7000 35.0 25 18 55Good Inventive 20 7000 35.0 9.5 18 55 Good Example

In Test Nos. 19 and 20, the inner layer portion 4 consisted of thecommercially pure titanium of JIS Class 2, and the first surface layerportion 2 and the second surface layer portion 3 consisted of a titaniumalloy containing Nb. Further, the porosity of the inner layer portion 4was less than 30%. In addition, the first surface layer portion 2 andthe second surface layer portion 3 had a thickness of 5 μm or more, andthis thickness was a sufficient thickness. Therefore, the oxidationweight gain in the heating at 700° C. for 200 hours was 25 g/m² or less,the oxidation weight gain in the heating at 750° C. for 200 hours was 70g/m² or less, and test No. 2 exhibited an excellent oxidationresistance.

Example 2-3

As shown in Table 7, for test No. 21, titanium alloy sheets consistingof Ti-1.0Cu-1.0Sn-0.35Si-0.25Nb were used, for No. 22, titanium alloysheets consisting of Ti-1.0Cu-0.5Nb were used, and for No. 23, titaniumalloy sheets consisting of Ti-0.25Fe-0.45Si were used, the package 6having 250 mm×1000 mm×4500 mm (thickness×width×length) was manufactured,thereafter the titanium lumps 7 consisting of the commercially puretitanium (briquette and titanium sponge) was supplied in the innerportion of the package 6, the package 6 was enclosed under a vacuumatmosphere at about 8×10⁻² Pa to be formed into the titanium material 5,and the titanium material 5 was used as a material for hot rolling.

Thereafter, this titanium material 5 was heated to 820° C. and subjectedto hot rolling to have a thickness of 5 mm, and thereafter, bothsurfaces of the titanium material 5 were subjected to descalingtreatment in which about 40 μm was removed per side (80 μm on bothsurfaces) using shotblast and nitric-hydrofluoric acid.

In addition, the titanium material 5 was subjected to cold rolling to beformed into a titanium composite material 1 having a thickness of 1 mm,and subjected to heat treatment in which the titanium material washeated to 600 to 700° C. and retained for 240 minutes in vacuum or in aninert gas atmosphere, as annealing treatment.

TABLE 7 Titanium material for hot working Titanium material Materialused as Interior Package degree of Test inner portion pure thicknessvacuum Chemical composition of package (mass %) No. of package titanium(mm) (Pa) Si Nb Al Ta Cu Sn Fe 21 Briquette + titanium JIS Class 2 14.08 × 10⁻² 0.35 0.2 — — 1.00 1.00 — sponge 22 Briquette + titanium JISClass 2 16.0 8 × 10⁻² — 0.5 — — 1.00 — — sponge 23 Briquette + titaniumJIS Class 2 14.0 8 × 10⁻² 0.45 — — — — — 0.25 sponge Titanium compositematerial Surface Outer layer Oxidation layer portion weight gain Testthickness ratio Porosity (g/m²) No. (μm) (%) (%) 700° C. 750° C.Producibility 21 48 4.8 0.09 20 59 Good Inventive 22 55 5.5 0.05 19 60Good Example 23 44 4.4 0.08 17 55 Good

In all of test Nos. 21 to 23, the first surface layer portion 2 and thesecond surface layer portion 3 contained one or more types of element ofSi and Nb. Further, the porosity of the inner layer portion 4 was lessthan 0.1%, and this was low. In addition, the first surface layerportion 2 and the second surface layer portion 3 had a thickness of 5 μmor more, and this thickness was a sufficient thickness. Therefore, theoxidation weight gain in the heating at 700° C. for 200 hours was 25g/m² or less, the oxidation weight gain in the heating at 750° C. for200 hours was 70 g/m² or less, and test No. 2 exhibited an excellentoxidation resistance.

Example 3 Example 3-1

As illustrated in FIGS. 1 and 2, the titanium materials 5 were each madeby packing the inner portion of the package 6 made of titanium alloysheets with the titanium lumps 7, a method for rolling these titaniummaterials 5 was performed, and thereby test specimens were manufactured.

Note that, the overall thickness of each titanium material 5 was 125 mm,the total content of Fe, Cr, Ni, Al, and Zr of the package 6 was 0.03 to1.1%, the chemical composition of the titanium lumps 7 in the innerportion fell within ranges of O: 0.030 to 0.33%, and Fe: 0.028 to0.086%, and was C: 0.01% or less, H: 0.003 or less, and N: 0.006% orless. In order to compare the influence of hot-rolling ratio, some ofthe titanium materials 5 having overall thicknesses of 25 mm or 50 mmwere manufactured.

Specifically, titanium alloy sheets having adjusted concentrations ofFe, Cr, Ni, Al, and Zr and an adjusted thickness were used in an outercircumference to manufacture the package 6, and the inner portion ofthis package 6 was packed with a compressed body (briquette) made bysubjecting a titanium sponge to compression molding, and thereafter, alid of the titanium material 5 was welded.

Some of the titanium materials 5 were manufactured by packing a titaniumsponge as it is without being formed into a briquette, and some of thetitanium materials 5 were manufactured by packing a briquette includingscraps which are mixed at 10% or 30% and made by cutting a pure-titaniumsheet having the same composition as that of a titanium sponge into anabout—25 mm square.

As to a welding method, in order to prevent the titanium lumps 7 frombeing oxidized or nitrided in hot working, electron beam welding wasperformed in a vacuum atmosphere in which the degree of vacuum of theinner portion of the titanium material 5 is made 10 Pa or less.

Thereafter, the titanium material 5 was subjected to hot rolling to havea thickness of 5 mm, and thereafter subjected to descaling (shotblastand pickling), cold rolling, and annealing to be formed into thetitanium composite material 1. Note that the thickness of the firstsurface layer portion 2 and the second surface layer portion 3constituting an element concentrating region (titanium alloy) wasadjusted depending on the thickness of the outside titanium alloy sheetsand a surface removal amount in the descaling.

As to each test material being the titanium composite material 1, aphase grain size, tensile strength, elongation, fatigue strength, andformability at different positions were evaluated under the followingconditions.

(Grain Size of α Phase)

The thickness of the first surface layer portion 2 and the secondsurface layer portion 3 was measured by an EPMA. On microstructurephotographs taken under an optical microscope, the average grain size ofα phases at positions of sheet thickness of 1 to 10% was calculated inthe inner layer portion and the surface layer portion by an interceptmethod in accordance with JIS G 0551 (2005).

(Tensile Strength, Elongation)

Tensile test materials were prepared in which a parallel portion was6.25×32 mm, a distance between gauge points was 25 mm, a chuck portionwas 10 mm in width and an overall length was 80 mm (size that was halfthe size of a JIS13-B tensile test material), and a tensile test wascarried out under conditions of an elastic stress rate of 0.5%/minbetween gauge points until a 0.2% proof stress measurement and 30%/minfrom the proof stress onward. In this case, the tensile strength andtotal elongation in a direction perpendicular to the rolling directionwere evaluated.

(Fatigue Strength)

A fatigue test was performed under conditions of a stress ratio R=−1 anda frequency of 25 Hz using the plane bending fatigue test materialillustrated in FIG. 3 and a plane bending fatigue testing machinemanufactured by Tokyo Koki Co. Ltd. The number of repetitions untilrupturing at respective stress amplitudes was determined to prepare astress fatigue curve, and a fatigue limit (fatigue strength) at whichrupturing did not occur even when bending was repeated 10′ times wasevaluated.

(Formability)

A titanium sheet that was worked into a shape of 90 mm×90 mm×0.5 mm wassubjected to a spherical stretch forming test using a spherical punch of40 mm using a deep drawing testing machine of model number SAS-350Dmanufactured by Tokyo Testing Machine Inc. For the punch stretch formingtest, a high viscosity oil (#660) manufactured by Nihon Kohsakuyu Co.,Ltd. was applied and a polyethylene sheet was placed thereon so that thepunch and titanium sheet did not directly contact, and evaluation wasperformed by comparison with a bulge height at a time when the testmaterial ruptured.

Since a bulging height in a spherical stretch forming test significantlyreceives the influence of oxygen concentration, if the bulging heightwas 21.0 mm or more in JIS Class 1, the bulging height was 19.0 mm ormore in JIS Class 2, or the bulging height was 13.0 mm or more in JISClass 3, the formability was determined as good (the mark “0” in thetable). If otherwise, the formability was determined as poor (the mark“x” in the table).

(Metal Microstructure)

FIG. 4 illustrates an example of microstructure photographs in the caseof manufacturing by the method described above. FIG. 4(a) is amicrostructure photograph of test No. 1 (Comparative Example, a commontitanium material), FIG. 4(b) is a microstructure photograph of test No.5 (Inventive Example of present invention), FIG. 4(c) is amicrostructure photograph of test No. 12 (Inventive Example of presentinvention), and FIG. 4(d) is a microstructure photograph of test No. 17(Inventive Example of present invention).

Note that FIG. 4(b) to FIG. 4(d) are Inventive Example of the presentinvention, and the thickness of the first surface layer portion 2 andthe second surface layer portion 3 differs.

The test results are collectively shown in Tables 8 and 9. Table 8 showsthe case of using a commercially pure titanium equivalent to JIS Class 1as the titanium lumps 7, and Table 9 shows the case of usingcommercially pure titaniums equivalent to JIS Classes 2 or 3 as thetitanium lumps 7. Further, the signs N1 to N4 in the column of “LEVEL OFMATERIAL FORM USED AS PACKAGE INNER PORTION” in Tables 8 and 9 indicatethe following kinds and ratios.

N1: Briquette including 100% of titanium spongeN2: 100% of titanium sponge as it isN3: Briquette including mixture of 90% of titanium sponge and 10% ofscrap having the composition equivalent to that of titanium spongeN4: Briquette including mixture of 70% of titanium sponge and 30% ofscrap having the composition equivalent to that of titanium sponge

TABLE 8 Conditions after hot rolling Titanium material for hot workingFinal Chemical composition of package sheet Level of Chemicalcomposition (mass %) Hot- thickness Final annealing material formInterior of titanium filler Alloy Oxygen rolling after cold conditionTest used as package pure (mass %) component concentration ratio rollingTemperature Time No. inner portion titanium O Fe Component Mass % Mass %(%) (mm) (° C.) (min) 1 (Melted ingot) JIS Class 1 0.043 0.029 — — — 961.0 580 240 2 (Melted ingot) JIS Class 1 0.043 0.029 — — — 96 1.0 660240 3 (Melted ingot) JIS Class 1 0.043 0.029 — — — 96 1.0 780 240 4 N1JIS Class 1 0.043 0.028 Fe  0.110 0.042 85 1.0 660 240 5 N1 JIS Class 10.043 0.028 Fe 0.11 0.042 90 1.0 660 240 6 N1 JIS Class 1 0.043 0.028 Fe0.11 0.042 96 1.0 580 240 7 N1 JIS Class 1 0.043 0.028 Fe 0.11 0.042 961.0 630 240 8 N1 JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 0.5 630 240 9N1 JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 0.5 630 240 10 N1 JIS Class1 0.043 0.028 Fe 0.11 0.042 96 1.0 660 240 11 N1 JIS Class 1 0.043 0.028Fe 0.11 0.042 96 1.0 660 240 12 N1 JIS Class 1 0.043 0.028 Fe 0.11 0.04296 0.5 660 240 13 N1 JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 0.5 660240 14 N1 JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 0.5 660 240 15 N1 JISClass 1 0.043 0.028 Fe 0.11 0.042 96 0.5 700 240 16 N1 JIS Class 1 0.0430.028 Fe 0.11 0.042 96 0.5 720 240 17 N1 JIS Class 1 0.043 0.028 Fe 0.110.042 96 0.5 630 240 18 N1 JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 0.5660 240 19 N1 JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 0.5 630 240 20 N1JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 0.5 630 240 21 N1 JIS Class 10.043 0.028 Fe 0.21 0.042 96 1.0 630 240 22 N1 JIS Class 1 0.043 0.028Fe 0.46 0.042 96 1.0 630 240 23 N2 JIS Class 1 0.043 0.028 Fe 0.11 0.04296 1.0 660 240 24 N3 JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 1.0 660240 25 N4 JIS Class 1 0.043 0.028 Fe 0.11 0.042 96 1.0 660 240 26 N1 JISClass 1 0.043 0.028 Al 0.22 0.042 96 0.5 680 30 27 N1 JIS Class 1 0.0430.028 Al 0.22 0.042 96 0.5 700 30 28 N1 JIS Class 1 0.043 0.028 Cr 0.410.042 96 0.5 660 240 29 N1 JIS Class 1 0.043 0.028 Ni 0.19 0.042 96 0.5660 240 30 N1 JIS Class 1 0.043 0.028 Zr 0.20 0.040 96 0.5 660 240 31 N1JIS Class 1 0.043 0.028 Fe0.03, Cr0.02, 0.040 96 0.5 660 240Ni0.05/total 0.1 32 N1 JIS Class 1 0.043 0.028 Fe0.05, Cr0.05, 0.040 960.5 660 240 Ni0.08/total 0.18 33 N1 JIS Class 1 0.043 0.028 Fe0.03,Al0.1, 0.040 96 0.5 660 240 Cr0.02, Zr0.07/ total 0.22 Titaniumcomposite material Surface layer portion Inner portion Surface AverageOuter layer Average Mechanical properties grain layer portion grainTensile Fatigue Fatigue Bulging Test size Porosity thickness ratio sizeElongation strength strength strength height No. (μm) (%) (μm) (%) (μm)(%) (MPa) (MPa) ratio (mm) 1 14 0 *  — * — * — 45 349 221 0.63 20.3Comparative 2 55 0 *  — * — * — 49 289 182 0.63 21.9 Example 3 300 0 * — * — * — 56 284 157 0.55 19.9 4 35 0   36 4 1 30 306 237 0.77 21.4Inventive 5 49 0.1  37 3.7 9 36 305 205 0.67 21.1 Example 6 10 0.02 393.9 5 34 341 251 0.74 21.2 7 32 0.02 22 2.2 5 39 308 236 0.77 21.2 8 350.01 19 3.8 5 38 310 238 0.77 21.4 9 33 0.01 37 7.4 5 34 321 242 0.7521.2 10 56 0.02 16 1.6 9 39 300 226 0.75 21.4 11 56 0.02 38 3.8 9 38 306233 0.76 21.4 12 56 0.01 38 7.5 9 35 309 240 0.78 21.5 13 59 0.01 19 3.810 42 300 230 0.77 21.4 14 59 0.01 38 7.5 10 40 306 229 0.75 21.3 15 730.01 19 3.8 14 44 297 226 0.76 21.7 16 98 0.01 34 6.8 5 46 296 227 0.7721.5 17 33 0.01 5 1.0 5 37 296 197 0.67 21.4 18 56 0.01 8 1.5 7 37 295200 0.68 21.4 19 33 0.01 48 9.6 5 34 330 242 0.73 21.3 20 33 0.01 8016.0 5 30 338 244 0.72 21.1 21 32 0.02 50 5.0 4 34 325 244 0.75 21.1 2232 0.02 51 5.1 3 32 326 248 0.76 21.1 23 55 0.02 37 3.7 9 39 305 2350.77 21.2 24 56 0.02 38 3.8 8 39 303 234 0.77 21.3 25 55 0.02 37 3.7 1038 304 234 0.77 21.4 26 37 0.01 20 4.0 6 38 306 225 0.74 21.1 27 47 0.0120 4.0 10 34 311 229 0.74 21.4 28 55 0.01 21 4.1 3 35 315 345 0.78 21.029 56 0.01 21 4.1 6 35 314 240 0.76 21.1 30 54 0.01 21 4.2 9 43 300 2310.77 21.3 31 56 0.01 20 3.9 8 43 302 232 0.77 21.2 32 55 0.01 20 4.0 640 306 235 0.77 21.1 33 55 0.01 21 4.2 5 39 309 236 0.76 21.1 The mark“*” indicates that the value fell out of the definition according to thepresent invention.

Test Nos. 4 to 33 in Table 8 were Inventive Example of the presentinvention that satisfied all of the conditions specified in the presentinvention, and test Nos. 1 to 3 were Comparative Examples that did notsatisfy the conditions specified in the present invention.

Test Nos. 1 to 3 were titanium alloy sheets equivalent to JIS Class 1and had formabilities and fatigue strengths that serve as standards forevaluating formabilities and fatigue strengths of the Inventive Exampleof the present invention. The fatigue strength ratios of test No. 1 to 3were 0.63, 0.63, and 0.55, respectively, and these were common values.

Test Nos. 4 to 33 acquired mechanical properties of elongation: 30 to46%, tensile strength: 295 to 341 MPa, fatigue strength: 197 to 251 MPa,fatigue strength ratio: 0.67 to 0.78, and bulging height: 21.0 to 21.7mm, and it is understood that test Nos. 4 to 33 were excellent in bothformability and fatigue strength.

TABLE 9 Conditions after hot rolling Titanium material for hot workingFinal Chemical composition of package sheet Level of Chemicalcomposition (mass %) Hot- thickness Final annealing material formInterior of titanium filler Alloy Oxygen rolling after cold conditionTest used as package pure (mass %) component concentration ratio rollingTemperature Time No. inner portion titanium O Fe Component Mass % Mass %(%) (mm) (° C.) (min) 34 (Melted ingot) JIS Class 2 0.082 0.056 — — — 961.0 660 240 35 (Melted ingot) JIS Class 2 0.082 0.056 — — — 96 1.0 700240 36 N1 JIS Class 2 0.082 0.058 Fe 0.10 0.090 96 1.0 630 240 37 N1 JISClass 2 0.082 0.058 Fe 0.10 0.090 96 1.0 660 240 38 N1 JIS Class 2 0.0820.058 Fe 0.10 0.090 96 1.0 700 240 39 N1 JIS Class 2 0.082 0.058 Fe 0.100.090 96 1.0 700 240 40 N1 JIS Class 2 0.082 0.058 Fe 0.45 0.092 96 1.0700 240 41 N1 JIS Class 2 0.082 0.058 Fe 0.10 0.090 96 1.0 700 240 42 N1JIS Class 2 0.082 0.058 Al 0.20 0.092 96 1.0 700 240 43 N1 JIS Class 20.082 0.058 Fe0.03, Al0.1, 0.091 96 1.0 700 240 Cr0.03, Zr0.07/ total0.23 44 (Melted ingot) JIS Class 3 0.180 0.050 — — — 96 1.0 660 240 45(Melted ingot) JIS Class 3 0.280 0.049 — — — 96 1.0 660 240 46 N1 JISClass 3 0.180 0.048 Fe 0.11 0.182 96 1.0 660 240 47 N1 JIS Class 3 0.1800.048 Fe 0.11 0.182 96 1.0 660 240 48 N1 JIS Class 3 0.180 0.048 Fe 0.110.182 96 1.0 660 240 49 N1 JIS Class 3 0.180 0.048 Fe 0.42 0.180 96 1.0660 240 50 N1 JIS Class 3 0.280 0.049 Fe 0.25 0.279 96 1.0 660 240 51 N1JIS Class 3 0.180 0.048 Al 0.20 0.179 96 1.0 660 240 52 N1 JIS Class 30.180 0.048 Fe0.04, Al0.1, 0.180 96 1.0 660 240 Cr0.04, Zr0.07/ total0.24 53 N1 JIS Class 4 0.301 0.052 Fe 0.24 0.309 96 1.0 660 240 Titaniumcomposite material Surface layer portion Inner portion Surface AverageOuter layer Average Mechanical properties grain layer portion grainTensile Fatigue Fatigue Bulging Test size Porosity thickness ratio sizeElongation strength strength strength height No. (μm) (%) (μm) (%) (μm)(%) (MPa) (MPa) ratio (mm) 34 39 0 *  — * — * — 31 358 207 0.58 19.2Comparative 35 65 0 *  — * — * — 33 339 199 0.59 20.1 Example 36 20 0.0242 4.2 10 26 398 275 0.69 19.2 Inventive 37 40 0.02 40 4.0 8 27 371 2800.75 19.8 Example 38 66 0.02 12 1.2 11 33 341 255 0.75 20.6 39 66 0.0240 4.0 12 31 365 272 0.75 20.2 40 65 0.02 43 4.3 6 30 364 280 0.77 20.141 66 0.02 80 8.0 11 25 378 284 0.75 19.3 42 66 0.02 40 4.0 11 26 365279 0.75 20.0 43 65 0.02 42 4.2 9 31 362 275 0.75 20.3 44 39 0   — * — *— 29 540 321 0.59 13.6 Comparative 45 38 0   — * — * — 26 602 348 0.5813.1 Example 46 41 0.02 10 1.0 9 27 546 379 0.69 13.5 Inventive 47 410.02 39 3.9 8 28 552 402 0.73 13.5 Example 48 41 0.02 79 7.9 9 25 563415 0.74 13.2 49 41 0.02 35 3.5 6 26 555 417 0.75 13.3 50 40 0.02 45 4.55 25 606 421 0.69 13.1 51 41 0.02 48 4.8 9 26 556 407 0.73 13.1 52 410.02 39 3.9 6 26 606 407 0.67 13.1 53 40 0.02 45 4.5 6 25 614 400 0.6510.0 The mark “*” indicates that the value fell out of the definitionaccording to the present invention.

Test Nos. 36 to 43 and 46 to 53 in Table 9 were Inventive Example of thepresent invention that satisfied all of the conditions specified in thepresent invention, and test Nos. 34, 35, 44, and 45 were ComparativeExamples that did not satisfy the conditions specified in the presentinvention.

Test Nos. 34 and 35 were titanium alloy sheets equivalent to JIS Class2, and test Nos. 44 and 45 were titanium alloy sheets equivalent to JISClass 3. Test Nos. 34, 35, 44, and 45 all had formabilities and fatiguestrengths that serve as standards for evaluating formabilities andfatigue strengths of the Inventive Example of the present invention. Thefatigue strength ratios of test Nos. 34 and 35 were 0.58 and 0.59,respectively, and the fatigue strength ratios of test Nos. 44 and 45were 0.59 and 0.58, respectively. These were all common values.

Test Nos. 36 to 43 and 46 to 53 acquired mechanical properties ofelongation: 25 to 33%, tensile strength: 341 to 614 MPa, fatiguestrength: 255 to 421 MPa, fatigue strength ratio: 0.65 to 0.77, andbulging height: 10.0 to 20.6 mm, and it is understood that test Nos. 36to 43 and 46 to 53 were excellent in both formability and fatiguestrength.

Example 4 Example 4-1

Titanium sponge (JIS Class 2, granularity=0.25 to 19 mm) produced by theKroll process was used as the titanium lump supplied into the package.Further, using β-type titanium alloy Ti-15V-3Cr-3Sn-3Al sheet products(thickness was 1 to 15 mm), rectangular parallelepipeds havingthicknesses of 45 to 80 mm, a width of 100 mm, and a length of 120 mmwere manufactured as the packages.

When manufacturing the package, first, five titanium sheets werepreassembled into a box shape, and thereafter, a titanium sponge wassupplied into the box shape, and an opening portion of the preassembledbox is covered with a titanium sheet. The preassembled titanium materialwas put inside a vacuum chamber, and the pressure of the vacuum chamberwas reduced to a predetermined pressure (vacuum), and thereafter seamsof the entire circumference were welded and sealed by an electron beam.The degree of vacuum inside the chamber at that time was made 8.7×10⁻³to 2.2×10⁻² Pa, as shown in Table 10.

By the processes described above, the packages the entire circumferenceof which is sealed with a β-type titanium alloy was formed, the innerportion of the package was packed with a titanium sponge, and thepressure of the inner portion of the titanium material was reduced tothe predetermined degree of vacuum.

The manufactured packages were heated to 850° C. in an air atmosphere,and thereafter subjected to hot rolling at working ratios at 92 to 97%as shown in Table 10 to be formed into hot-rolled sheets havingthicknesses of 4.8 to 5.0 mm. Next, the packages were subjected toannealing in a vacuum atmosphere at 600 to 650° C., for 4 to 10 hours.In addition, the packages were subjected to shotblast and pickling toremove scale layers.

Further, to enable cross-sectional observation, the produced titaniumcomposite sheets were embedded in resin and subjected to polishing andetching, and thereafter observed with an optical microscope and thethickness of the surface layer portion was measured. This measuredthickness of the surface layer portion was divided by the overallthickness of the titanium composite material to be calculated as asurface layer portion ratio.

In order to calculate a proportion of pores remaining in a pure titaniumportion of the titanium composite material (hereinafter referred to asporosity), a sample was embedded in a resin such that the cross sectionof the sample can be observed, thereafter polished and subjected tomirror finish, and thereafter, optical micrographs were taken at 500×magnification. The area proportion of pores were calculated from thetaken optical micrographs, the measurement results of five micrographswere averaged and calculated as the porosity.

For comparison with the titanium composite material according to thepresent invention, a 5 mm sheet product of the commercially puretitanium (JIS Class 2) was used.

Titanium sheets of the titanium composite materials according to thepresent invention and the Comparative Example were exposed to a 1 vol. %H₂+99 vol. % Ar atmosphere, which is a hydrogen absorbing environment,at 500° C. for 5 hours.

After the exposure, impact test specimens of 4.8 to 5 mm×10 mm×55 mm andhaving a 2 mm V notch were manufactured, with the longitudinal directionthereof being a rolling direction and the sheet thickness penetratingdirection thereof being the direction of the notch. Next, hydrogenembrittlement was evaluated using an impact value that is a valueobtained by dividing an impact energy absorption of the Charpy impacttest by the cross-sectional area of the test specimen. Here, because theimpact value of a pure titanium Class 2 product before the exposure tothe hydrogen absorbing environment was 2.5×10² J/cm², a case where theimpact value after the exposure decreases from 2.5×10² J/cm² by 20% ormore, that is, a case where the impact value after the exposure was lessthan 2.0×10² J/cm² was determined as the occurrence of the hydrogenembrittlement.

The results of the above are collectively shown in Table 10.

TABLE 10 Titanium material for hot working Titanium composite materialTitanium Surface Titanium material Hot- layer Package material degree ofrolling portion Test thickness thickness vacuum ratio ratio PorosityImpact value No. (mm) (mm) (Pa) (%) (%) (%) (×10² J/cm²) 1 — 60 — 92 — *0 * 1.4 Comp. Ex. 2 2 60 8.7 × 10⁻³ 92 3.3 0.2 2.5 Inventive 3 5 60 9.2× 10⁻³ 92 8.3 0.2 2.3 Example 4 8 60 2.2 × 10⁻² 92 13.3 0.1 2.1 5 5 808.9 × 10⁻³ 94 6.3 0.1 2.4 6 10 80 1.9 × 10⁻² 97 12.5 0.1 2.2 The mark“*” indicates that the value fell out of the definition according to thepresent invention.

Test No. 1 was an example of a commercially pure titanium Class 2product produced without using the package. Under the influence of theexposure to the hydrogen environment, the impact value was less than2.0×10² J/cm², and this was low.

In contrast, test Nos. 2 to 6 that satisfied the specifications of thepresent invention resulted in impact values of 2.0×10² J/cm² or more,and these were high.

Example 4-2

Examples in which the alloy kind of the package was changed with respectto Example 4-1 are described. The sheet thickness of titanium sheetsusing for the package was 3 mm, the overall thickness of the titaniummaterials was 60 mm, sheet thicknesses after the hot rolling were 4.8 to5.0 mm, and the remainder of the sample manufacturing was performed by amethod similar to that of Example 4-1. Table 11 shows the examples.

TABLE 11 Titanium material for hot working Titanium composite materialTitanium Surface material layer Interior degree of portion Test pureChemical composition of Mo vacuum ratio Porosity Impact value No.titanium package equivalent (Pa) (%) (%) (×10² J/cm²) 7 JIS Class 2Ti—15Mo—2.7Nb—3Al—0.2Si 15.8 8.7 × 10⁻³ 5 0.2 2.3 Inventive 8 JIS Class2 Ti—3Al—8V—6Cr—4Mo—4Zr 9.3 9.2 × 10⁻³ 5 0.3 2.4 Example 9 JIS Class 2Ti—20V—4Al—1Sn 13.3 8.7 × 10⁻³ 5 0.2 2.1

Test Nos. 7 to 9 satisfied the specification of the present inventionand therefore resulted in impact values of 2.0×10² J/cm² or more, andthese were high.

Example 4-3

Examples in which the kind of a titanium sponge to be supplied waschanged to JIS Class 3, with respect to Example 4-1, are described. Thesheet thickness of titanium sheets using for the package was 3 mm, theoverall thickness of the titanium materials was 60 mm, sheet thicknessesafter the hot rolling were 4.8 to 5.0 mm, and the remainder of thesample manufacturing was performed by a method similar to that ofExample 4-1.

Because the impact value of JIS Class 3 used here was 0.5×10² J/cm², animpact value decreasing from 0.5×10² J/cm² by 20% or more, that is, animpact value of 0.4×10² J/cm² or less was determined as embrittlement byhydrogen. Table 12 shows the examples.

TABLE 12 Titanium material for hot working Titanium composite materialTitanium Surface material layer Interior degree of portion Test pureChemical composition of Mo vacuum ratio Porosity Impact value No.titanium package equivalent (Pa) (%) (%) (×10² J/cm²) 10 JIS Class 3 — —— — * 0 * 0.3 Comp. Ex. 11 JIS Class 3 Ti—15V—3Cr—3Al—3Sn 10 8.7 × 10⁻³4 0.2 0.5 Inv. Ex. The mark “*” indicates that the value fell out of thedefinition according to the present invention.

Test No. 10 was an example of a commercially pure titanium Class 3product produced without using the package. Under the influence of theexposure to the hydrogen environment, the impact value was less than0.5×10² J/cm², and this was low.

Test No. 11 satisfied the specification of the present invention andtherefore resulted in impact values of 0.5×10² J/cm², and these werehigh.

Example 5 Example 5-1

Neutron shielding sheets of test Nos. 1 to 24 shown in Table 13 wereproduced by the following method.

TABLE 13 Titanium material for hot working Titanium composite materialTitanium B content Surface Occurrence material of surface layer rate ofMaterial used as Interior Package degree of layer portion crack inNeutron Test inner portion pure thickness vacuum portion ratio PorosityCrack bending test shielding No. of package titanium (mm) (Pa) (mass %)(%) (%) evaluation (%) effect 1 — JIS Class 1 4 8 × 10⁻³ — — * 0.5 Nocrack 0 1.0 Comp. Ex. 2 Briquette JIS Class 1 20 8 × 10⁻³ 0.5 5 0.7 Nocrack 0 12.4 Inventive 3 Briquette + titanium JIS Class 1 10 8 × 10⁻³3.0 5 0.8 No crack 0 13.5 Example sponge 4 Briquette + titanium JISClass 1 10 8 × 10⁻³ 2.2 20 0.5 No crack 0 44.3 sponge 5 Briquette +scrap JIS Class 1 10 8 × 10⁻³ 1.5 40 0.4 No crack 0 73.1 6 Scrap +titanium JIS Class 1 10 8 × 10⁻³ 0.9 40 9.8 No crack 0 63.7 sponge 7Briquette + titanium JIS Class 1 10 8 × 10⁻³ 0.4 40 30.0 No crack 0 52.1sponge 8 Briquette + titanium JIS Class 1 4 8 × 10⁻³ 0.1 5 0.6 No crack0 1.9 sponge 9 Briquette + titanium JIS Class 1 4 8 × 10⁻³ 1.5 15 0.5 Nocrack 0 11.3 sponge 10 Briquette + titanium JIS Class 1 4 8 × 10⁻³ 2.340 0.2 No crack 0 34.2 sponge 11 Briquette + titanium JIS Class 2 20 8 ×10⁻³ 0.8 5 0.8 No crack 0 15.4 sponge 12 Briquette + titanium JIS Class2 10 8 × 10⁻³ 1.4 5 0.9 No crack 0 8.9 sponge 13 Briquette + titaniumJIS Class 2 10 8 × 10⁻³ 0.5 25 0.3 No crack 0 29.7 sponge + scrap 14Briquette + titanium JIS Class 2 10 8 × 10⁻³ 0.1 40 0.2 No crack 0 43.7sponge + scrap 15 Briquette + titanium JIS Class 2 4 8 × 10⁻³ 1.2 5 0.7No crack 0 3.9 sponge + scrap 16 Briquette + titanium JIS Class 2 4 8 ×10⁻³ 1.9 15 0.4 No crack 0 12.4 sponge + scrap 17 Briquette + titaniumJIS Class 2 4 8 × 10⁻³ 2.6 40 0.3 No crack 0 36.4 sponge + scrap 18Briquette JIS Class 3 20 8 × 10⁻³ 1.2 5 0.7 No crack 0 17.6 19Briquette + titanium JIS Class 3 10 8 × 10⁻³ 2.5 5 0.9 No crack 0 12.5sponge + scrap 20 Briquette + titanium JIS Class 3 10 8 × 10⁻³ 1.7 150.3 No crack 0 28.4 sponge + scrap 21 Briquette + titanium JIS Class 310 8 × 10⁻³ 2.0 40 0.2 No crack 0 83.1 sponge + scrap 22 Briquette +titanium JIS Class 3 4 8 × 10⁻³ 1.3 5 0.7 No crack 0 4.0 sponge + scrap23 Briquette + titanium JIS Class 3 4 8 × 10⁻³ 1.9 20 0.4 No crack 016.4 sponge + scrap 24 Briquette + titanium JIS Class 3 4 8 × 10⁻³ 0.840 0.3 No crack 0 22.1 sponge + scrap The mark “*” indicates that thevalue fell out of the definition according to the present invention.

First, Ti—B alloy sheets for the package 6 were manufactured by hotrolling ingots made by adding B in advance using TiB₂ or ¹⁰Bconcentrated boron (H₃ ¹⁰BO₃, ¹⁰B₂O¹⁰B₄C) and melting. After the hotrolling, the Ti—B alloy sheets were subjected to strip running through acontinuous pickling line consisting of nitric-hydrofluoric acid, andoxide scales on the surfaces of the hot-rolled sheets were removed.

These Ti—B alloy sheets were subjected to electron beam welding under avacuum atmosphere of about 8×10⁻³ Pa in such a manner that the alloysheets were welded at positions corresponding to five faces of the slab,and thereby the hollow package 6 was manufactured.

One or more types of material selected from a titanium sponge, abriquette by compressing a titanium sponge, and titanium scraps cut into30 mm×30 mm×30 mm or smaller were put in the inner portion of thepackage 6, and the remaining one face of the slab was similarlysubjected to the electron beam welding, and thereby the titaniummaterial 5 having a thickness of 100 mm and including the inner portionbeing vacuum was manufactured.

Note that, by changing the thickness of the alloy sheets, the ratio ofthe surface layer portion with respect to the overall thickness of thehot-rolled sheet can be adjusted.

FIG. 5 is a schematic diagram of the titanium material 5 including thetitanium lump 7 packing within the package 6 that was made slab-like byassembling the Ti—B alloy sheets in this way.

Using steel manufacture facility, this titanium material 5 was heated at800° C. for 240 minutes and thereafter subjected to hot rolling, andthereby strip coils having thicknesses of about 4 to 20 mm wereproduced.

The strip coils after the hot rolling were subjected to strip runningthrough a continuous pickling line consisting of nitric-hydrofluoricacid, scarfed by about 50 μm per side, and thereafter subjected tovisual observation on an occurrence situation of a crack. Note that, asto a method for measuring the depth of the surface layer portion (Bconcentrated layer), portions of the hot-rolled sheet after the picklingwere cut out (at three spots of a front end, middle and, rear end in thelongitudinal direction, extracted from the width-direction-centerportions, respectively), polished, and subjected to SEM/EDS analysis,and the proportion of the surface layer portion with respect to thesheet thickness and the B content of the surface layer portion wasdetermined (the average value in an observation spot was adopted).

Further, with respect to the front end, center and rear end as the threelocations in the longitudinal direction, a total of 20 bending testspecimens in the L-direction were extracted from a central portion inthe width direction, and a bending test was performed in accordance withJIS Z 2248 (metallic materials bend test method). The test temperaturewas room temperature, a bending test at bending angles up to 120 degreeswas performed using the three-point bending test, and the presence orabsence of crack occurrence was evaluated to determine the crackoccurrence rate.

Furthermore, to evaluate the neutron shielding effect, Am—Be (4.5 MeV)was used as a radiation source, and a test specimen having dimensions of500 mm×500 mm×4 to 20 mm thickness was fixed at a position that was 200mm from the radiation source. A detector was installed at a positionthat was 300 mm from the radiation source, a radiation equivalent withrespect to a peak value of target energy was measured respectively forcommercially pure titanium of JIS Class 1 as a control test specimen (4mm thickness) and the test specimen (4 to 20 mm thickness), and theneutron shielding effect was evaluated based on the ratio between themeasured values (the value for each test specimen is described for acase where the neutron shielding effect of commercially pure titanium ofJIS Class 1 is taken as “I”).

The results are shown collectively in Table 13.

Comparative Examples and Inventive Example of the present invention oftest Nos. 1 to 10 were a case where the kind of a base metal was thecommercially pure titanium JIS Class 1.

Test No. 1 being a Comparative Example was a case where a commerciallypure titanium not containing B was used as the package 6, rather thanTi—B alloy sheets. There was no crack or the like occurring on thehot-rolled sheet, and no crack occurred in a bending test.

Test No. 2 being Inventive Example of present invention was a case wherea titanium material 5 having a thickness of 100 mm was subjected to hotrolling to have a thickness of 20 mm. The ratio of the first surfacelayer portion 2 and the second surface layer portion 3 was 5%, the Bcontent of the first surface layer portion 2 and the second surfacelayer portion 3 was 0.5%, therefore there was no crack occurring on thehot-rolled sheet, and no crack occurred in a bending test.

Test Nos. 3 to 7 were a case where a titanium material 5 having athickness of 100 mm was subjected to hot rolling to have a thickness of10 mm, and the ratio, B content, and porosity of the first surface layerportion 2 and the second surface layer portion 3 were changed. The ratioof the first surface layer portion 2 and the second surface layerportion 3 fell within a range of 5 to 40%, the B content of the firstsurface layer portion 2 and the second surface layer portion 3 fellwithin a range of 0.1 to 3.0%, therefore there was no crack occurring onall of the hot-rolled sheet, and no crack occurred in a bending test.

Test Nos. 8 to 10 were a case where a titanium material 5 having athickness of 100 mm was subjected to hot rolling to have a thickness of4 mm, and the ratio and B content of the first surface layer portion 2and the second surface layer portion 3 were changed. The ratio of thefirst surface layer portion 2 and the second surface layer portion 3fell within a range of 5 to 40%, the B content of the first surfacelayer portion 2 and the second surface layer portion 3 fell within arange of 0.1 to 3.0%, therefore there was no crack occurring on all ofthe hot-rolled sheets, and no crack occurred in a bending test.

Inventive Example of the present invention shown as test Nos. 11 to 17were a case where the kind of a base metal was the commercially puretitanium JIS Class 2.

Test No. 11 was a case where a titanium material 5 having a thickness of100 mm was subjected to hot rolling to have a thickness of 20 mm. Theratio of the first surface layer portion 2 and the second surface layerportion 3 fell within a range of 5 to 40%, the B content of the firstsurface layer portion 2 and the second surface layer portion 3 fellwithin a range of 0.1 to 3.0%, therefore there was no crack occurring onthe hot-rolled sheets, and no crack occurred in a bending test.

Test Nos. 12 to 14 were a case where a titanium material 5 having athickness of 100 mm was subjected to hot rolling to have a thickness of10 mm, and the ratio or B content of the first surface layer portion 2and the second surface layer portion 3 were changed. The ratio of thefirst surface layer portion 2 and the second surface layer portion 3fell within a range of 5 to 40%, the B content of the first surfacelayer portion 2 and the second surface layer portion 3 fell within arange of 0.1 to 3.0%, therefore there was no crack occurring on all ofthe hot-rolled sheets, and no crack occurred in a bending test.

Test Nos. 15 to 17 were a case where a titanium material 5 having athickness of 100 mm was subjected to hot rolling to have a thickness of4 mm, and the ratio or B content of the first surface layer portion 2and the second surface layer portion 3 were changed. The ratio of thefirst surface layer portion 2 and the second surface layer portion 3fell within a range of 5 to 40%, the B content of the first surfacelayer portion 2 and the second surface layer portion 3 fell within arange of 0.1 to 3.0%, therefore there was no crack occurring on all ofthe hot-rolled sheets, and no crack occurred in a bending test.

Inventive Example of the present invention of test Nos. 18 to 24 were acase where the kind of a base metal was the commercially pure titaniumJIS Class 3.

Test No. 18 was a case where a titanium material 5 having a thickness of100 mm was subjected to hot rolling to have a thickness of 20 mm. Theratio of the first surface layer portion 2 and the second surface layerportion 3 fell within a range of 5 to 40%, the B content of the firstsurface layer portion 2 and the second surface layer portion 3 fellwithin a range of 0.1 to 3.0%, therefore there was no crack occurring onthe hot-rolled sheets, and no crack occurred in a bending test.

Test Nos. 19 to 21 were a case where a titanium material 5 having athickness of 100 mm was subjected to hot rolling to have a thickness of10 mm, and the ratio or B content of the first surface layer portion 2and the second surface layer portion 3 were changed. The ratio of thefirst surface layer portion 2 and the second surface layer portion 3fell within a range of 5 to 40%, the B content of the first surfacelayer portion 2 and the second surface layer portion 3 fell within arange of 0.1 to 3.0%, therefore there was no crack occurring on all ofthe hot-rolled sheets, and no crack occurred in a bending test.

Test Nos. 22 to 24 were a case where a titanium material 5 having athickness of 100 mm was subjected to hot rolling to have a thickness of4 mm, and the ratio or B content of the first surface layer portion 2and the second surface layer portion 3 were changed. The ratio of thefirst surface layer portion 2 and the second surface layer portion 3fell within a range of 5 to 40%, the B content of the first surfacelayer portion 2 and the second surface layer portion 3 fell within arange of 0.1 to 3.0%, therefore there was no crack occurring on all ofthe hot-rolled sheets, and no crack occurred in a bending test.

In addition, as a result of the evaluation by the technique describedabove, although the neutron shielding effect could not be confirmed ontest No. 1 being a Comparative Example, all of Nos. 2 to 24 beingInventive Example of the present invention exhibited neutron shieldingeffects of 1 or more, and the neutron shielding effect could beconfirmed.

Note that, a stainless steel sheet having a B content of 0.5%, used fora nuclear fuel storage rack, (4 mm thickness) exhibited a neutronshielding effect of 23.7. Test Nos. 4 to 7, 10, 13, 14, 17, 20, and 21exhibited neutron shielding effects higher than the neutron shieldingeffect of this stainless steel sheet.

Example 5-2

Neutron shielding sheets of test Nos. 25 to 34 shown in Table 14 wereproduced by the following method.

TABLE 14 Titanium material for hot working Titanium composite materialTitanium B content Surface Occurrence material of surface layer rate ofMaterial used as Interior Package degree of layer portion crack inNeutron Test inner portion pure thickness vacuum portion ratio PorosityCrack bending test shielding No. of package titanium (mm) (Pa) (mass %)(%) (%) evaluation (%) effect 25 Briquette + titanium JIS Class 1 10 8 ×10⁻³ — — * 0.1 No crack 0 1.0 Comp. Ex. sponge + scrap 26 Briquette +titanium JIS Class 1 5 8 × 10⁻³ 2.4 5 0.1 No crack 0 5.5 Inventivesponge + scrap Example 27 Briquette + titanium JIS Class 1 20 8 × 10⁻³1.5 20 0.1 No crack 0 14.8 sponge + scrap 28 Briquette + titanium JISClass 1 40 8 × 10⁻³ 2.8 40 0.2 No crack 0 36.0 sponge + scrap 29Briquette + titanium JIS Class 2 5 8 × 10⁻³ 3.0 5 0.2 No crack 0 6.2sponge + scrap 30 Briquette + titanium JIS Class 2 20 8 × 10⁻³ 0.5 200.2 No crack 0 10.3 sponge + scrap 31 Briquette + titanium JIS Class 240 8 × 10⁻³ 1.9 40 0.1 No crack 0 31.9 sponge + scrap 32 Briquette +titanium JIS Class 3 5 8 × 10⁻³ 1.3 5 0.2 No crack 0 4.0 sponge + scrap33 Briquette + titanium JIS Class 3 20 8 × 10⁻³ 2.7 20 0.1 No crack 018.8 sponge + scrap 34 Briquette + titanium JIS Class 3 40 8 × 10⁻³ 0.140 0.1 No crack 0 14.6 sponge + scrap The mark “*” indicates that thevalue fell out of the definition according to the present invention.

By a similar procedure of Example 5-1, a Ti—B package 6 having differentsheet thickness and chemical composition were assembled, and a titaniummaterial 5 having a thickness of 100 mm and including the inner portionpacked with a titanium sponge and cut scraps was manufactured.

Using steel manufacture facility, this titanium material 5 was heated at800° C. for 240 minutes and thereafter subjected to hot rolling, andthereby strip coils having a thickness of about 5 mm were produced.

The strip coils after the hot rolling were subjected to strip runningthrough a continuous pickling line consisting of nitric-hydrofluoricacid, in addition, the titanium material was subjected to cold rollingto be formed into a titanium sheet having a thickness of 1 mm, subjectedto heat treatment in which the titanium material was heated to 600 to750° C. and retained for 240 minutes in vacuum or in an inert gasatmosphere, as annealing treatment, and thereby a titanium compositematerial 1 was manufactured.

The titanium composite material 1 being a cold-rolled sheet subjected tovisual check to observe an occurrence situation of a crack in a surfaceinspection process after the annealing. Note that, as to a method formeasuring the depth of the first surface layer portion 2 and the secondsurface layer portion 3 (B concentrated layers), portions of thetitanium composite material 1 were cut out (at three spots of a frontend, middle, and rear end in the longitudinal direction, extracted fromthe width-direction-center portions, respectively), polished, andsubjected to SEM/EDS analysis, and the proportion of the first surfacelayer portion 2 and the second surface layer portion 3 with respect tothe sheet thickness of the titanium composite material 1 and the Bcontent of the first surface layer portion 2 and the second surfacelayer portion 3 were determined (the average value in an observationspot was adopted).

Further, with respect to the front end, center and rear end as the threelocations in the longitudinal direction, a total of 20 bending testspecimens in the L-direction were extracted from a central portion inthe width direction, and a bending test was performed in accordance withJIS Z 2248 (metallic materials bend test method). The test temperaturewas room temperature, a bending test at bending angles up to 120 degreeswas performed using the three-point bending test, and the presence orabsence of crack occurrence was evaluated to determine the crackoccurrence rate.

Furthermore, to evaluate the neutron shielding effect, Am—Be (4.5 MeV)was used as a radiation source, and a test specimen having dimensions of500 mm×500 mm×1 mm thickness was fixed at a position that was 200 mmfrom the radiation source. A detector was installed at a position thatwas 300 mm from the radiation source, a radiation equivalent withrespect to a peak value of target energy was measured respectively forcommercially pure titanium of JIS Class 1 as a control test specimen (1mm thickness) and the test specimen (i mm thickness), and the neutronshielding effect was evaluated based on the ratio between the measuredvalues (the value for each test specimen is described for a case wherethe neutron shielding effect of commercially pure titanium of JIS Class1 is taken as “1”).

The results are shown collectively in Table 14.

Comparative Examples and Inventive Example of the present invention oftest Nos. 25 to 28 were a case where the kind of a base metal was thepure titanium JIS Class 1.

Test No. 25 being a Comparative Example was a case where a commerciallypure titanium not containing B was used as the package 6, rather thanTi—B alloy sheets. There was no crack or the like occurring on thecold-rolled sheet, and no crack occurred in a bending test.

Test Nos. 26 to 28 being Inventive Example of the present invention werea case where the ratio, B content, and porosity of the first surfacelayer portion 2 and the second surface layer portion 3 were changed. Theratio of the first surface layer portion 2 and the second surface layerportion 3 fell within a range of 5 to 40%, the B content of the firstsurface layer portion 2 and the second surface layer portion 3 fellwithin a range of 0.1 to 3.0%, therefore there was no crack occurring onall of the cold-rolled sheets, and no crack occurred in a bending test.

Inventive Example of the present invention of Test Nos. 29 to 31 were acase where the kind of the base metal was the pure titanium JIS Class 2,and the ratio, B content, and porosity of the first surface layerportion 2 and the second surface layer portion 3 were changed. The ratioof the first surface layer portion 2 and the second surface layerportion 3 fell within a range of 5 to 40%, the B content of the firstsurface layer portion 2 and the second surface layer portion 3 fellwithin a range of 0.1 to 3.0%, therefore there was no crack occurring onall of the cold-rolled sheets, and no crack occurred in a bending test.

Inventive Example of the present invention of Nos. 32 to 34 were a casewhere the kind of the base metal was the pure titanium JIS Class 3, andthe ratio, B content, and porosity of the first surface layer portion 2and the second surface layer portion 3 were changed. The ratio of thefirst surface layer portion 2 and the second surface layer portion 3fell within a range of 5 to 40%, the B content of the first surfacelayer portion 2 and the second surface layer portion 3 fell within arange of 0.1 to 3.0%, therefore there was no crack occurring on all ofthe cold-rolled sheets, and no crack occurred in a bending test.

In addition, as a result of the evaluation by the technique describedabove, although the neutron shielding effect could not be confirmed ontest No. 25 being a Comparative Example, all of Nos. 26 to 34 beingInventive Example of the present invention exhibited neutron shieldingeffects of 1 or more, and the neutron shielding effect could beconfirmed.

REFERENCE SIGNS LIST

-   1 Titanium composite material-   2 First surface layer portion-   3 Second surface layer portion-   4 Surface layer portion-   5 Titanium material for hot working-   6 Package-   7 Titanium lump

1. A titanium composite material comprising: a first surface layerportion; an inner layer portion; and a second surface layer portion;wherein: the first surface layer portion and the second surface layerportion consist of a titanium alloy; the inner layer portion consists ofa commercially pure titanium including pores; a thickness of at leastone of the first surface layer portion and the second surface layerportion is 2 μm or more, and a proportion of the thickness with respectto an overall thickness of the titanium composite material is 40% orless; and a porosity in a cross section perpendicular to a sheetthickness direction is more than 0% and 30% or less.
 2. The titaniumcomposite material according to claim 1, wherein at least one of thefirst surface layer portion and the second surface layer portion has achemical composition comprising, by mass %: platinum group elements:0.01 to 0.25%, rare earth elements: 0 to 0.2%, Co: 0 to 0.8%, Ni: 0 to0.6%, and a balance: Ti and impurities.
 3. The titanium compositematerial according to claim 2, wherein: the platinum group elements arePd and/or Ru.
 4. The titanium composite material according to claim 2,wherein the chemical composition contains, by mass %: rare earthelements: 0.001 to 0.2%.
 5. The titanium composite material according toclaim 2, wherein the chemical composition contains, by mass % one ormore elements selected from: Co: 0.05 to 0.8%, and Ni: 0.05 to 0.6%. 6.The titanium composite material according to claim 1, wherein thecommercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.
 7. A titaniummaterial for hot working, comprising: a package; and one or more typesselected from a titanium sponge, a briquette obtained by compressing atitanium sponge, and a commercially pure titanium scrap, with which thepackage is packed, wherein a portion of the package consists of atitanium alloy, the portion constituting an outer layer after hotworking.
 8. The titanium material for hot working according to claim 7,wherein the titanium alloy has a chemical composition comprising, bymass %, platinum group elements: 0.01 to 0.25%, rare earth elements: 0to 0.2%, Co: 0 to 0.8%, Ni: 0 to 0.6%, and a balance: Ti and impurities.9. The titanium composite material according to claim 3, wherein thechemical composition contains, by mass %: rare earth elements: 0.001 to0.2%.
 10. The titanium composite material according to claim 3, whereinthe chemical composition contains, by mass % one or more elementsselected from: Co: 0.05 to 0.8%, and Ni: 0.05 to 0.6%.
 11. The titaniumcomposite material according to claim 4, wherein the chemicalcomposition contains, by mass % one or more elements selected from: Co:0.05 to 0.8%, and Ni: 0.05 to 0.6%.
 12. The titanium composite materialaccording to claim 9, wherein the chemical composition contains, by mass% one or more elements selected from: Co: 0.05 to 0.8%, and Ni: 0.05 to0.6%.
 13. The titanium composite material according to claim 2, whereinthe commercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.
 14. Thetitanium composite material according to claim 3, wherein thecommercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.
 15. Thetitanium composite material according to claim 4, wherein thecommercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.
 16. Thetitanium composite material according to claim 5, wherein thecommercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.
 17. Thetitanium composite material according to claim 9, wherein thecommercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.
 18. Thetitanium composite material according to claim 10, wherein thecommercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.
 19. Thetitanium composite material according to claim 11, wherein thecommercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.
 20. Thetitanium composite material according to claim 12, wherein thecommercially pure titanium has a chemical composition comprising, bymass %, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% orless, Fe: 0.5% or less, and a balance: Ti and impurities.